If there are snipers about, do not remain in one place for too long.
You can jump back to walls you have actually currently embarked on to stay clear of obstacles.
In the end-of-level scraps, get anything with a gun prior to you handle the others.
Guns
To give yourself the best chance in the end-of-level battles look to take out anything which has a gun first before dealing with anything else.
Obstacles
You can avoid obstacles by jumping towards walls you have already jumped off.
Snipers
Try and keep on the move and not stay in one place for too long otherwise will you run the risk of being picked off by snipers.