getting better?

I am a really keen surfer and have been surfing for about 4 years.The only problem is i only get to go when the school holidays come as i live in london. I know a lot about surfing from research and cant wait to move to the coast when i finish up school. I haven't seemed to improve that much and my first sessions are always rubbish
and i only get the hang of things when its at the end of the holidays which usualy last a week, mainly in Ireland. Is there any way to keep up my techniques whilst not at the sea or is pratice the only way to improve.
any advice would be great

any advice would be great
