I know how you feel. I'm in high school, and I'm a major procrastinator. Not specifically about ponies, but in general. My recommendation, in addition to what Gone Airbourne said, is to make a schedule for yourself, and then stick to it.
Currently, I just make a schedule in my head on a day by day basis, which is hard to stick to. I'm determined to stick to my schedule today, though. Today, I got home from school about 30 minutes ago. I'm going to use the computer for no more than 30 more minutes for leisure, and then I'm going to do my Spanish 2 and my Pre-Calculus homework. Then, I'll use the computer for a few hours, and then read more out of A Scarlet Pimpernel while I eat dinner for my Advanced English 10 class. Then I'll take a bath, and if I have time I'll use the internet some more, and then go to bed at 9 pm so I'll hopefully get about 9 hours of sleep for school tomorrow.
I've never been into sports and rarely have I been into school activities at all, so most days of the week outside of school is my free time. However, I do usually attend taekwondo class on Mondays and Wednesdays. On Sundays I usually go to church and then to a bible study in the evening. Every once and awhile there will be a church youth group on Saturday, probably around once a month. I'm not a Christian anymore, I believe in a non-religious spirituality, but I still enjoy going to church, youth group, and bible study.
I list my priorities to myself in my head when I feel like I need to make sure that I'm keeping them straight, because it's really tempting to choose fun over everything else, which is what I do most of the time.
I'm working to get my priority list to look something like this:
1. Parents and friends (both IRL friends and internet friends)
2. Spirituality
3. My Health
4. School work / job (when I hopefully get a job for the first time this summer)
5. Free time*
(*5 consists of many things that are very important to me. For example, watching My Little Pony: Friendship is Magic and participating in MLP Forums ties into #2. I just have daily responsibilities that I need to take care of first.)
So, you could do something like that: list your priorities, write them down and read it every day. There is absolutely nothing wrong with loving to use the internet, MLP forums, etc. It's just very important to keep balance. I know this, because of how unbalanced my life often is, and how I realize how much balance would help.