Make sure the baking powder is newish, it doesn't store well. Handle the dough as little as possible. Don't roll out too thin. My mum says scones like to be close together on the tray to rise (--but she is a crazy Swedish lady--).
Scones can be tricky to get right first time. You have to be really careful to not over handle the dough (just bring the ingredients together and pat out; the less you mess with it, the better). Make the scones quite thick (about 2cm), and when you cut it out, go straight down (don't twist the cutter). If using and egg wash, be careful to put it on the top and not let it dribble down the sides.
Once you've got the hang of it you'll be whipping up a fresh batch of scones whenever you have friends round for tea!