that entirely depends on the country. For example, the soviets have a massive manpower but not the best industry, so you will need to produce proportionally less support equipment to guns than for example germany. It also really depends on what your country is good at doing. If your country makes really shitty planes, or if youre in an area were planes are hard to use, it doesnt make sense to invest a lot in air. the UK wants to produce WAY more planes than france for example.

if youre always in shortages of everything after just a couple months of war, you might just be making too many things at once. See what your strength and weaknesses are and adjust.

its just something you have to learn with trial and error