Ok, that map is rocket arena on farewell.
Become familiar with the blast radius of the rocket explosion, so you can hit your enemies without hitting yourself.
You can detonate rockets mid-air by right clicking, but a direct hit is the most powerful.
Try to shoot rockets at the spawnpoints, and above the jump in the middle (a blind spot for your enemies while they're going up it). You have unlimited ammo, so spam everything with rockets
Those bots are fast. Be faster
Here's my demo on that level:
http://filebox.vt.edu/users/dmaz/campaign_19_demo.pk3 in which I barely beat the level after playing badly
To view, place file in Nexuiz/data and start from the Demos menu at the bottom of the menu screen.