The Second World War was the most deadly war so far, exceeding even the Taiping Rebellion, the First World War and probably even the 1918 flu pandemic with its death toll.
The death toll would likely not have been changed much by improvements to the survivability of ground troops, but such improvements would have affected the chance of not coming out of the war as losing country (I won't call that "winning"). The high attrition rates especially of infantry were a major concern and had a huge impact on the course of almost all longer campaigns.
Surprisingly (or not; depends on how much you believe in mankind's intelligence), several opportunities for increasing the survival chances (= increasing the days in combat until permanent incapacitation or death) were somewhat to entirely neglected. I attempted to compile a list here, admittedly with a huge bias towards criticising the Wehrmacht, for my sources are most detailed about this one:
(1) Dig quick, deep and often: German post-War (50's, 60's) military literature was not short of criticism regarding the diligence of German troops in fortifying, especially in comparison to the "Russians" (Soviets). German troops were often caught by indirect fire while resting.
(2) Camouflage well: Quite the same can be said about the German inclination towards shoddy camouflage. This neglect is already evident in imagery from pre-war exercises*. Again, the "Russians" served as example.
(3) Make use of microterrain: I am amazed by the quantity of pre-war and wartime photos that depict an anti-tank gun on open ground, such as on a street. There's not even a hint of trying to become less visible. the only advantage was probably that running away was no option on such terrain, so the crew had to fight (or surrender).
Infantry survival against competent opponents depends largely on the skilled use of microterrain (small elevations and depressions, shadows, concealment and above-surface cover).
The German army - supposedly champion of the exploitation of microterrain since the introduction of Stoßtrupp tactics in 1916 - did not maintain a high standard in this regard.
(4) Use fragmentation protection vests. practical vests had been developed during the First World War already, the lack of even basic torso protection was a horrible negligence. Fragmentation protection vests are usually credited with a 50% reduction in overall personnel losses after introduction of the steel helmet.
(5) Use more lightly armoured personnel carriers: The typical APC of WW2 was a half-track vehicle with 6-14.5 mm thick armour plating. This was meant to be machine gun-proof and the German experience was apparently a 50% reduction of infantry losses on the attack (German SdKfz 250 and 251 APCs were more elaborate, more off-road-mobile and more reliably bullet-proofed than the U.S. M3 half-tracks) on top of enabling attacks where normal infantry couldn't attack.
The production cost was about 1/5th to 1/3 of a normal tank, the fuel consumption was even smaller and in worst case normal trucks could be equipped with half-track drive and some armour plating to further reduce the costs. Germany neglected this as much as the production of normal trucks - and even wasted many half-tracks on specialist functions instead of focusing their employment on the APC role.
(6) More mobile, elusive infantry tactics. Infantry had to fight from field fortifications or with armour support if it was to succeed on open, flat ground as in the Ukraine. The same does not apply to terrains with short lines of sight. German infantry doctrine was well into the 1960's too rigid and too oriented towards field fortification. The Soviets understood this and exploited it in their breakthrough battles of 1943-1945 by application of incredible artillery fire densities. No detected field fortification was of any use against this avalanche unless leaders were skilled and lucky enough to shift between a primary and a secondary position in time to dodge the fires.
(7) Shortcomings regarding anti-tank gun quality up to 1942 and quantity from 1942-1945 as well as the rather late introduction of shaped charge-based portable anti-tank stand-off munitions was an obvious survivability problem. Tank commanders usually did not dare to close in with infantry late in the war; early on there was nothing keeping them at bay.
(8) The lack of radios at company and platoon level was pandemic. Only the U.S. Army had a somewhat decent radio equipment. Early portable radios were far from reliable, long-ranged or trouble-free, but they were extremely useful whenever they functioned. A platoon with radio contact could cooperate with another platoon instead of fighting alone. it could also call for indirect fires instead of being forced to solve tactical challenges with riskier tactics. It is a great disappointment that Germany - a county with a very good electrical industry and many electrical tech pioneers - wasn't able to supply its army with enough portable practical radio sets.
(9) Insufficient infantry training. The German army insisted successfully on a thorough education and training of its officers and non-commissioned officers. It did not manage to follow its better judgement in regard to infantrymen training. Six weeks training for infantry was simply inadequate. Poorly-trained infantry replacements were hardly a major relief for the front troops. These largely incompetent infantrymen (actually rather infantryboys) had little combat value, but required much attention and leadership by the veterans and NCOs. They died quickly, too. It would clearly have been better to insist on a thorough infantry training. This would have reduced the quantity of NCOs available at the front and would have delayed all infantry replacements by a few weeks to a few months, but the advantage would still already have set in by late 1942.
(10) Insufficient winter equipment. I suppose there's no real elaboration necessary.
(11) Individual weapon quality. Taking the German example, which was the most egregious; Germany had a practical, reliable and effective assault rifle ready by 1938 (Vollmer Maschinenkarabiner M35). Of course, it didn't introduce such a near-optimal infantry weapon until 1943 in any noticeable quantity.
(12) Emphasis on flanking fires. The German army has understood the superiority of flanking fires ever since 1915, but it did not include this fully into its doctrine until, well, let's better not get agitated about it again. Details are here.
(13) Sniper training. Snipers are not really 100% infantry, but they're a huge threat to it, and shortcomings in both sniper training and sniper equipment (no good sniper scope available until about 1942, not enough available ever during WW2) meant that there weren't enough effective snipers to counter hostile snipers.
(14) Neglect of artillery. Both production of field howitzers and production of their ammunition did cost German infantry dearly. The huge production of heavy anti-air guns was part of the reason, but the neglect went beyond this. Too much attention was wasted on inefficient heavy artillery and not enough attention was paid to the potential of artillery fire support in general. Field artillery was well established, but nowhere near in doctrinal importance to U.S. or Soviet field artillery. Germans did not solve tactical problems with much artillery fire often until there wasn't enough infantry left any more. Post-war it was understood that spending more iron was smarter than spending more blood, and the German army clearly had underestimated the virtues of brutish indirect firepower. The "3rd generation warfare" crowd around Lind et al enshrined this mistake as a virtue, but that's an exaggeration meant to combat an exaggeration of the importance of firepower over small unit action in the U.S. army. There's not just one mistake possible, the balance was delicate and changing depending on the campaign situation.
15) Stupid creation of ever new formations, even air force field formations. The creation of Waffen-SS and Luftwaffe divisions for employment as regular army divisions was stupid. neither had the mid-level or low-level leadership competence for this. The regular army could have created much better formations with most of the same personnel because of its better competence pool. The Waffen-SS had excessive casualty rates during 1941-1942 and its divisions became effective only later, when its leaders had gained experience and approximated the army's better tactics. The Waffen-SS's reputation of an elite force is nonsense. It had dropped its high recruitment standards by 1943, was more (overly) aggressive on the tactical level and the only truly powerful Waffen-SS divisions were merely counterparts of a couple of similarly lavishly equipped and reinforced army divisions. Preferred access to personnel and material in an army of shortages = elite division - no matter Waffen-SS or not.
The Luftwaffe field divisions were even worse. their senior commanders had served as army officers more than a decade ago and some troops were trained by some of the few surviving old paratroopers, but the competence for land warfare was still marginal. thee divisions broke easily, were quite useless on the offence, usually poorly equipped (often times with captured weapons dating back to WW1) and generally a waste of personnel. The army suffered from a shortage of good age (18-30) and good intelligence personnel, the air force had it - and wasted it in incompetent formations. The reasons were entirely of political nature.
Finally, the army itself was forced to raise far too many divisions. There were 35 waves of new divisions overall. To put this in context: Even as early as 1940, creating the 5th to 9th wave of new divisions faced serious criticism because of the huge drop in quality due to age structure, short training and the inadequate leader pool.
In short: It would have been possible to prolong the misery of the common infantrymen for operational-level gains if less mistakes were made.
*: Hence my occasional insistence that a good ground combat demo can be heard, but not seen. Sadly, our army still demonstrates ground combat with lots of visible troops doing stuff in line of sight of VIPs who in turn get a completely wrong picture of what competent ground combat looks like. This is an international shortcoming, of course..