YouTube has a lot of great information and here I have found one on surfboard repairs. It takes you through all the necessary steps you need to follow to clean up all your dings and cuts.
One thing you should think about though before fixing your board is whether you think you can do as good a job of repairing it, as a surfboard shaper would be able to do. This is important as, if you cannot, the chances are that your repair will impact the dynamics of your surfboard and therefore, your own performance in the water. If this is the case, it is highly recommended that you get a surfboard shaper to repair your surfboard.
Time is always another critical factor. Do you have the time and the care to do all the little things, that make the difference between a shoddy and a beautiful job? If not, again, give the job to someone who does. Your surfing will thank you