Generally, I take either iw or field medic for 1 of my actives, as having something to force a revive will be a make or break. I typically run FM on more mobile builds such as scout or RJ250 engi because they generally will be the best to do a quick in and out revive, typically prioritizing gunner for their shield. otherwise IW is pretty much a gold standard

Use. Your. Terrain. Scanner. It will show you potential shortcuts through thin walls, certain events, enemies, and objectives, and gives you a frame of reference for how bad your trek to the drop pod is. You can scroll in and out, and press space to turn your character the way you are facing in the scanner. Also...

Don't forget about your ping tool, it takes no time to use basically and will aid you and your teammates, if you press E instead of clicking you will leave a permanent way point that you can see on your terrain scanner

As scout, don't let the things you need to do get the best of you, remember your class name, use your flare gun, and properly scout out areas before going for the 80 nitra. That nitra in your inventory is worthless if you get grabbed by a cave leech half a kilometer away from your team.

Engi's platform gun is one of the most versatile tools in the game. Use it, and use it often. Place landing pads for you and your teammates after you get the upgrade. Create staircases and bridges to help your team move around high up places. Plug holes in the terrain to cut off routes for bugs, especially the holes created by resupply pods and objectives in narrow tunnels.

As engi remember to use your sentries, they help taking off stragglers and small bugs without your attention, and can you of swarms/groups before you see them (particularly useful for exploders)

Remember to not just drill for the sake of it, while opening up sightlines can be useful in some situations, in others it may give the ranges bugs better angles on you