Clownfish wise I would probally avoid a maroon clown. They have a tendancy to be aggressive towards other fish, anemones (to eager to be in them and rough) and also with you when you go to clean the tank! ;-)
Depending on your tank size, certain tangs can be good beginning fish. I would avoid tangs like the powder blue and the powder brown since they have a tendancy to be more suseptable to diseases.
If you are doing a fish only tank, certain triggers do well. If you are doing a reef with no shrimp you can do a grouper as well. Just look up the sizes and such as te groupers and triggers (some) do get large.
Invert wise the best one to start with in my opinion are the mushrooms. Feather dusters.They are relativly easy and you can easily judge how well they are doing in your tank. Once you have your tank up and running, with appropriate lighting and your water balanced, you should be able to handle whateevr your light is specified for. Just remeber to add slowly, especially to a new tank. Also, for certain corals, proper additives are necessary! Research the specific needs of the corals such as calcium,lighting, and water movement.
My best advice would be to post a list of fish/corals you are interested in and then have us all comment on it. A lot of the time people in the LFS dont know, and we may have had personal experiences that can help you avoid a mistake.
Hope this helps a little
Lexi