If it's your first time running through the campaign, don't do the tech tree blind. I'm not an amazing rts player and I genuinely needed to abandon my first two campaigns because I just prioritized the wrong techs and made the missions unwinnable.
You will be severely punished on quite a few missions if you don't have the Ballista and Tesla towers unless you have god gamer status micro abilities and apm or know what to expect in the mission. Both towers have aoe attacks that can single handedly hold waves back if they're placed strategically. Also, the train resource techs are insanely powerful because it's just a free resource drop every in-game day and you can get things like iron to make soldiers without needing to secure a resource node. Later in the game, snipers are better than soldiers in every way. Get a deathball of them and win.
Besides standard eco/expansion rts advice, one thing the game doesn't necessarily tell you is that there is a hidden "noise" value of actions that attracts zombies. Rangers make very little noise and soldiers make a lot. Noise accumulates on a per-tile basis so a military unit that is standing still will slowly accumulate noise(even if they aren't firing), but if you set them to patrol a few tiles there will be little to no noise accumulation. Besides that, just make sure you wall up and maybe have a few fallback points you can defend at because this is a game where if a single zombie manages to get through your patrols you lose the entire mission. It's really rewarding to play, but also super frustrating (and time consuming) to learn.