Hi, it depends where in dorset you are. But there are lots of great venues and clubs on our door step. If you are able to transport your wheels then i can recommend blackmore vale trials club and yeovale mcc. They have good beginner routes. But there are plenty of others. Either use this site, amca website and the acu website to find clubs and trials that are coming up. Or trials and motorcross news (paper)
Places to practice are few and far between. Most these days use the trials to practice. But if you travel there are purpose built practice grounds in surrey which are amazing. (Hook woods)