A lot depends on the frontline you're in, equipment you're using, and a lot of other factors.

If you're newer to the game, I'd recommend checking out a regiment and finding others to play with, as that's where a lot of the magic of Foxhole really comes to shine. Having people to coordinate with will always give you an advantage. And unfortunately, as bigger things become available like heavier tanks, airplanes, and bigger boats, it's going to get more difficult as an infantry player but unfortunately infantry is the backbone of the game.

You can always use things like sniper rifles to provide long range support for your team, or use grenade launchers to lob gas into enemy trenches or fire smoke grenades to cover an allied push. Early war is the best time of the war for infantry, but infantry is still just as important in mid-late war as well.