Only just having played a few campaign missions and skirmish matches, I like to build an extra group of engineers at the start and start taking the different points for more resources. Then I get a squad of infantry and start expanding as well, for myself, I usually go for the fuel points first because fuel is quite important because you need that to build more buildings and some units (Which will help you earlier to get better units such as tanks).
Some people get a sniper earlier on to harass the enemies infantry and engineer squads while they are trying to expand. Having at least one sniper is a usually good idea but I haven't had that much time to test out a few strategies I have using a few.
Again, I am REALLY new to this game but I am quite familiar with RTS games. This is using the american team. I've never played any other faction yet.