Practise sailing up to an improvised start line until you can hit the line at full speed on the starting signal. The first leg of the course is nearly always set to windward. It is here that your skill at sailing close-hauled will be tested. If you find that you are sailing slowly compared to other boats around you, look at how they have their sails set and the way they sail their boats and try to copy them.
Take the RYA Start Racing course and join a club that races dinghies, keelboats or multihulls and get some experience crewing for others before you buy your own boat.