Well, upload quality content and make sure it's appealing! It may be hard to get started. Here is a list of things you can do, along with some info:
Projects- Easy to do if you are a good builder. The project needs A LOT of effort put in it though to make it worthy, and if it is very good, you can get a lot of exp.
Texture Packs- Though will almost always generate a good amount of exp, it requires a lot of dedication and good art skills.
Skins- Unless you are well known or have mad skills, it is hard in this field. Your submission will be overflowed with spam skins or will have the attention swiped away by a better skin made by a well known person.
Servers- Not a good place for exp. I don't recommend using it as an exp source.
Blogs- Fairly easy, you just need very nice pics and a good main idea. The writing has to be organised and easy to read. Also, it has to be long, not a paragraph written in size 5 font.
Mods- Hard, considering the skills you will need, yet if your mod is good you will get rewarded nicely.
So, that's about it. Stay active in chat and the forums, make friends to help you, and post good content to get more subs.
Once you get a popular upload, you will get subs, which will help make future uploads even more popular, getting you even more subs. The cycle goes on and on if you are lucky!
