Warhammer 40,000: Battlesector

Explosives are king for most early 'Nid mobs. They are reusable after a cool down and they are a guaranteed hit against everyone on the tile, so they can wipe out Gaunts pretty well.

Unless there is a timer go for the Xcom bounding movement followed by overlapping field of fire on overwatch. Don't be afraid to do a very narrow overwatch cone to ensure that you are hitting the Nids at a good distance to inflict damage rather than the first second you see them.

Melee units are decent in a scrap but their real benefit is that their ability to effectively threaten squares and get good opportunity attacks.

You'll unlock plasma guns before you strictly need them, but you will need them. Armor in this game is no joke and if you don't have a way around it then your team is going to get stomped by a single heavily armored Nid. This also applies to skills that give AT damage like Krak grenades.

Following up on that, building your teams around being able to kill individual boss Nids/small squads is important. Swarming, easy to take down Nids are a problem but due to the grid playing field it's easy to funnel them into a killing field. However, if you end up with a one-sqaure threat like a Synapse creature then the map will start to work against you because you'll need to fan out to get good firing angles on the beast, opening you up to attack.