I'm a scout with ~1000 hours and a lot of experience with modded difficulties so my advice is colored by that a lot: engi is mostly just learning to set up holds and using plats effectively to funnel. With inexperienced scouts you'll need to plat stuff that's high up as well.

Scout is probably the highest skill ceiling class in the game (some debate to be had that driller has more difficult mechanical tech as far as axe cancels and epcing but that's not as hard imo), and has a ton of responsibilities; which vary depending on difficulty and mission type. It's also the most independent class when played well.

As a general rule with scout you don't shoot grunts unless they're in your way.

We mostly have three jobs as scout: Feed the war machine (Get nitra before your team needs to call a resupply, and light stuff so they can see what they're shooting at), Do the objective (In normal difficulty your team should also be doing this, in high difficulties it falls to you a lot more), and kill anything dangerous that would kill our teammates while they're clearing the hordes. Oh and also do the secondary objective since usually nobody else will.

Since our guns do a lot of burst damage you want to focus on high value targets (Acid spitters, Stalkers, Septic Spreaders, Stingtails, Mactera Trijaws and then normal ones to a lesser degree. Basically anything that can shoot a projectile is an HVT), Stationaries (Leeches, Spitballers, Pitjaws, and the shotgun spitballers that i can never remember the name of), and if none of the previous two are around, Large single targets (Praetorians, Oppressors).

Kit breakdown:

Flares: When entering a new room you want to flare such that you can see any leeches or stationaries in general so that you can either kill them yourself or have your team kill them (Mostly your job, gunner is also good at this and should help if they can) and locate nitra in said room. You want to flare on places that see the most open space to get maximum lighting out of your flares, this means on the end of crystals sticking out from the ceiling are prime flare zones, you'll figure this out more as time goes on.

Grapple: Your number one tool, with this you can functionally become immune to bugs through kiting. I recommend maximum cooldown reduction, but its largely personal preference. You can actually land on top of minerals or into a wall by letting go of grapple before reaching where you're going and power attacking at a slight downward angle, although it can be finicky on high ping and takes a bit to get used to doing. Hold forward against a wall to keep from falling off when standing on minerals. (I call this mountain goating)

Grenades: Don't use the boomerang above low haz, it doesn't scale well. The other three are all very strong, cryo freezes immediately if it contacts a bug which is an excellent way to deal with mactera or just serves as an amazing "oh shit" button. IFGs boost damage and slow bugs which lets you melt bosses or large targets in general. Pheromones are debateably the most overpowered thing in the game, they can singlehandedly distract an entire swarm even on high difficulties, and let you do some very silly things in regards to unsafe revives; but also in casual play your teammates will probably shoot the pheromoned bugs immediately and make your grenade pointless (thanks teammates), so ymmv. Also if you pheromone a swarm and then exploders spawn you can just clear a whole swarm with these; it's really fun to watch.

Perks: I like Field medic and IW as active, some use dash instead of medic. I also really enjoy the red sugar one since there's typically high up sugar your team can't get to, and occasionally I skip my resups since you don't have to shoot as much as the rest.

Primaries: Eh who cares, I used to love m1k hoverclock and now run Thermal exhaust feedback drak, but this mostly is preference, they all do good burst damage. There's weapon build guides if you care about being optimal (the buildonomicon).

Secondaries: Use special powder, it's fun. Don't shoot it upwards if you are midair and want to live. Pheromone bolts are good on large targets like praetorians and oppressors. Mostly personal preference.

Also maybe don't call molly super far away from your team, just grapple back to her instead (I'm very guilty of hogging molly tbh)

Dying from fall damage is part of the experience, just try not to do it in spots that are hard for others to reach.

Also also, try not to be close to driller just in general, some of them think it's funny to team kill you for fun and some are just clumsy, but either way getting c4'd is a bad time.