If you can get some brewing software it really makes designing beers a lot more fun. Good software will allow you to see changes in color and gravity as you play around with recipes. They will have BJCP guidelines for styles to help guide you. Really fun just to make stuff up or for when you make those "leftover beers".
When you're ready to test yourself try making an American Lager with rice or corn. You can use flakes but you get better flavor if you do a cereal mash. Light beers are the true test of a good brewer and hey, Summer is coming and you might need a good lawnmower beer!