Unfortuneatly this is a question that will have to be self tought just to ask "help on a new tank?'' well we could go on for hours. One thing i will suggest it to buy the book The New Marine Aquarium by Michael S. Paletta (20$) it is a great way to start off. there are may articles on the web to read. just read anything you can get your hands on. a small tank is by no means difficult. you just need to make sure of a few things
1. Know basics of SW care.
2. Dont overstock the tank
3. The key is the Live Rock and Live Sand.
4. Replace evoporated water with RO/DI. Chek daily to every other day.
5. water change 2X amonth
Other than that there isnt much else to do. Now after this post i might get some objection but i know from personal exp. I maintain 5 diff tanks under 20gallons. If you are content on getting a small tank try to get one with a built in filteration like the 12 gal sold on
www.aquariumpros.com it is under 200 and has an intregrated overflow and wet dry filter. i have this model and currently have several soft corals thriving in it as well as a few small fish( percula clown, neon goby) it has been set up for 2 years and all water parameters are perfect. i dont dose with any additives just what is replenished through the water changes. But like i said earlier know what you are doing and you will be fine. these tanks require far less care than my 47 gal and 300. good luck to you and before you leave read my signature.