You need a cohesive collection of artwork, and should have a portfolio of at least 10, no more than 25 great pieces of art.
In that portfolio, you should also have a 1 page artist biography about you and your process and message. Then you'll need an artist statement, a few sentences about your body of work.
And of course, a contact sheet of how the gallery can contact you and find you online.
Once you have that together, call or email to set up appointments to visit with curators and/or gallery owners.
I recommend researching the galleries to see if your work would be a good fit - it should be similar to other work they exhibit, but also different enough to get noticed.
As for actual exhibits, solo exhibits should have around 15-30 pieces (depending on the size and needs of the gallery), and group exhibits you'll probably have 3-5 pieces (depending on size and needs of gallery, and number of other artists involved, and size of your work).
Most galleries do not help with cost of framing of the work, though many galleries these days are also frame shops, and I'm sure would be happy to frame your work - at a price. That's something you'd have to ask during your gallery visits.
And always remember - be yourself, and stay true to you and your art. Always read the fine print, always get everything in writing. Don't get swindled by fees on top of fees on top of commissions. And lastly, enjoy the process - it's hard work, but is a really great experience to exhibit your art!!!!! :)