just some very basic things to keep in mind that have always helped me, even though i never really stayed only at the baseline...
1) before worrying about footwork, when you are coming in for whatever reason ALWAYS ALWAYS ALWAYS try to keep the racquet head above your wrist. this means really getting into knee bends when you get some low balls. i used to have some pretty scuffed up knees learning to stay down for the low ones.
2) you were right (sort of) about the firm wrist. it is more of a firm wrist and steadying squeeze of the racquet handle a split second before you are about to hit.
3) it is MUCH easier to keep racquet out in front of you at all time when coming in for a volley. reason being you really dont need to "swing" per say with a volley. it is much easier to move your body into the ball and as you do so let the racquet begin to "cup" the ball. also, remember to keep the head of the racquet ahead of your wrist as well as it will greatly increase the feel of stability of the shot with your weight moving into it as well.
as far as footwork goes a ton of small quick steps to set up are the best way, and is exactly the same thing you should do at the baseline as well. the final foot work would be to begin to turn your body to whichever side you are hitting on (forehand/backhand) and step across further in that direction into the ball. lastly, continue to move in on the ball after you make contact meaning take another few small steps.
and the final step is get into the net as much as possible, this will help you get accustomed to it. rally with some people and just constantly come in every chance. it will help develope your confidence for a match.