Customised clothing does seem to sell well - especially 'rocker' and 'goth' (I am too old to know about these things) and abstract art also sells.
Search for completed listings for similar things and see how well they've done.
There is nothing to stop you listing one or two items to test the market - but get some feedback first. Don't get feedback by buying ebooks and other sorts of rubbish - buy proper stuff you need over a period of a couple or three months. In the meantime, research your market and prepare a couple of items for sale.
If you are doing clothing - large sizes seem to do well, especially if it is something 'different' . Fetish and so on. But don't attempt this market if you have no affinity towards larger people - you will need to know what suits.
Art is good but awkward to post. Unless you are able to roll it into tubes.
But 'completed listings' in the box on the right of your ebay search is the key. You will know how well things sell for, how many have bid and the prices.
Good luck!