Skins get you barely any exp (unless they are done well), because the majority on PMC get less than 10 views per day, after they've left the "recently updated" column.
So I'd recommend doing an adventure. Just put your heart and soul into it! Make it good, and spend, say, a month doing it. Then post weekly updates so people know about it (I am doing this at the moment), then do a big launch and the exp should flood in!
Or you could do a texture pack, however this is VERY time consuming (trust me, i know) and unless it's done well, it will only gain you a few levels. - But can be rewarding if done to a high standard, and can top you up to level 20 in no time!
Hope this helps
Peace out.