Conquest Advice (in general)

Before you ask: My generals are Guderian, Rommel, Konev, Arnim, Pavlov, Leeb, and Horton.

Anyway, my main 3 issues (regardless of year or country) are:

  1. I'll take over my respective region, but after that, progress slows severely. (I'm also very cautious about putting out my best generals, mostly because I usually don't have access to a level 3 factory)

  2. I'll admit, resource spending is difficult for me. I tend to blow through it keeping units on the field.

  3. 9/10 times, my allies get jumped and I find myself on the back foot because I have to defend my base as well as managing my campaign.

Primarily, what should I focus on more in the beginning and later on?