First, the basics.

Start with your keyword research, obviously. The more niche you go, the easier it will be to rank for your keywords, but you have to balance that with what people are actually searching for. So start with ranking for niche keywords, and then after about 6 months start trying to rank for more competitive phrases. Here is a sample of Art related keywords and their searches per month, taken from keyworddiscovery:

As you can see, the keywords vary widely. Your next step is to look at the competition for each phrase:

• Query    Searches    Occurrences    KEI    Predicted Daily
• art    4991193    856000000    1.12    275256.32
• clip art    1915477    6560000    5.13    105621.61
• free clip art    1584938    908000    7.11    87404.05
• fine art    1341763    129000000    1.69    73997.53
• art galleries    1228954    2200000    5.88    67757.26
• art supplies    920197    1400000    6.09    50747.49
• body art    880042    281000    7.81    48533.2
• art gallery    765096    29600000    2.62    42192.28
• framed art    538714    1560000    5.44    29691.61

Obviously, if you own a body art store, you will want to try and rank for that quickly, and also go for your local phrases as well. Then, once you have all of your pages built with all of your keywords, submit your sitemap to Google Webmaster Tools, (you have to have a gmail account to do that) and you should get indexed in no time.