tips on growing flowers from seed

If by "prick out the top leaves", John, you intend to snip them off then you don't. Pricking out is a peculier term and means taking the seedlings from the original seed pot and replanting them in another pot with a stronger compost. The first two 'leaves' to appear are cotyledons and you don't do anything until the next two appear.These are true leaves and you can prick out and pot on as soon as they are large enough to handle.

Thanks for your usefull advice. but my flowers are getting very "leggy" and I want them to be sturdy before I plant them out. Have you any suggestions?

Pinching doesn't make the plants sturdier if there isn't enough light to begin with. They just develop more leggy side branches, gradually turning into a bowl of spaghetti!