What do I use to lube the valves and slides?

Also how do you stop making a nasty sound when playing?:confused:

You can buy valve oil for your horn at any music store. Vaseline works well as a slide lubricant.

As for the 2nd part of your question -- it's like asking how do you get to Carnegie Hall? Practice, practice, practice. You may want to try different mouth pieces - perhaps the one you're using isn't the best for you.