A 'body' of work is important. So often we are presented with a very mixed bag of artworks by one artist. Choose your best pieces and offer images of them either as good quality photographs in a folder or in an email. Each week we are approached by quite a few artists and it can be frustrating if artists just turn up in work hours expecting to be seen with no appointment and a bundle of artworks casually presented. Don't be disillusioned by rejection. No one likes to be told 'no thanks' and we all know how that feels but usually the gallery owner knows what will sell and what they are wanting. It's not a personal thing! Remember that you might paint very well but it does not mean it will be appropriate for all the galleries you approach.
Be realistic about the value of your work. This usually happens in consultation with the owner unless you already an established artist in which case you will be able to come to a quicker decision. It is very unprofessional to have completely differing prices at a variety of galleries. Very often artists are keen to sell at any cost which reduces your chances of getting into a good gallery. Make sure that you don't have them displayed in cafes or public spaces at drastically reduced prices to the ones that are set at the gallery. Clients are not happy if they purchase at top dollar only to see their artist selling at a discount somewhere else. Trade me is a definite 'put off' - don't fall into the trap of dollar reserves. Recently, we were approached by an artist who had rather good work only to discover easily on an internet search that they sold on face book for a pittance! Be careful at auctions that a reserve is placed on works. Accept that galleries have to charge a commission and be clear what that is and if it includes GST or website promotion. As an artist and a gallery owner I can know see both sides of the coin. Grumbling about commissions is not helpful- there are many costs associated with running a gallery. These include advertising, staff, rent, printing etc but galleries are usually the spaces that most clients come to to see a selection of art - it's a two way thing. Come up with a simple agreement which will prevent problems down the track. If you are accepted, ensure you get a consignment note on delivery.
Stick to deadlines, present your work completely finished. Check that the work is ready to hang - very often wasted time is taken up making the artworks safe to hang. Check that your frames are in good order, no one will buy a damaged piece of work. Good luck!