Many of your enemies will shoot at you. Progress slowly to avoid running into their projectiles. Jump out of the firing line then hold the fire button to automatically eliminate your enemies.
Disguises
After leveling new disguises will become available. Each offers a different bonus when equipped. For example, the Block disguise increases Knife and Uzi damage by 25% and the Indie disguise gives you an extra heart . If you have a particularly strong weapon, use a disguise that matches it.
Floaters
To take out the purple skull Floaters, stand on a flat platform at a fair distance and wait. The Floaters will eventually move into a lineup for an easy shot.
Weapon crates
When given an objective to collect weapon crates, keep killing enemies and they will eventually drop.