Some things I will tell you by listing some of them ;)
1. Enjoy what you do it makes a difference when you enjoy what you are promoting.
2. There is thousands of opportunities online and always be more for years to come before you join one do some research on the program or what ever it is.See what other people are saying and so on.
3. When you do join a online business,affiliate program or what ever make sure to do everything for that business or what ever it is you are promoting.Do not jump from opportunity to opportunity as they come this will only stop you from getting the money you desire to make and in the long run be a waste of time.
Do one thing at a time for whatever you are in once you do everything for that business then if you want look for another opportunity.there are times when you join a bad opportunity but there is also trial and error.
4. expect trial and error when marketing online i figure i put this since i said something about it in the other part lol but you should expect it and think of ways to make it work before you give up.
5. Track your ads this is most important and save you a lot of time and money.this will tell you where you are getting conversions and where you are not and also helps with split testing.
6. You must understand SEO this is a must! Most your traffic will come from the search engines.
7. Never give up as you see most if not all of the big name marketers did not start out making hundreds of thousands some even millions.They face all the things I listed but never gave up they found ways to make things work and there reward was true success.
I could probably write you a hub for each and make a list but them are some tips to keep in mind for what ever online business you are into.