I wouldn't know where to begin with this one. There's just so much to it. If you pay as much attention to the types of places you want to play in as the Owners do to the types of acts they want to hire, you'll find your niche.
As a general rule, if you're not turning down the odd gig then you're either not charging enough or not picky enough. I hope that makes sense to you.
As for the right way to ask... I prefer to make a phone call. You can arrange to meet if you want but in most cases, it's just not necessary. If your music is on your web-site, the manager/owner can scroll down and check you out while you're talking or as soon as you hang up.
As for CDs & Demos...... Don't get me started.