to the forum, Gareth
My main piece of advice, for starters, would be to read up on fishless cycling. You need to build up a colony of good bacteria in your filter that eat the fish's wastes for you and stop the water becoming toxic, and the best way to do that is with a fishless cycle; that way you grow the bacteria before you add any fish to the tank. The alternative is a fish-in cycle, which can make your fish very sick, or even kill them, while the bacteria grow.
Second, decide if there are any fish you really must have, and make sure you buy a tank that is big enough for them! There's nothing worse than having your heart set on a fish and finding out your tank's not large enough until after you've spent your hard earned cash on it!
Lastly; ask loads of questions on here. A lot of the people (not all, of course, but many) who work in fish shops are just doing it as a job, and their ultimate aim is to part you from your money. Many are also not up to date on the latest research and techniques in the hobby, at least in our member's experiences.
Here we have no axe to grind, no profit to be made, and we have some very knowledgeable experts who will help you with your choices