This is an ancient question, with a very good answer:

http://www.gamedev.net/page/resources/_/technical/game-programming/how-do-i-make-games-a-path-to-game-development-r892

-Tetris
-Breakout
-Pacman
-Mario

In that order, for very good reasons. It's going to be a lot harder than you might expect, and when you're done, you'll be ready to do any 2D game you want - or ready to step into 3D development.

Don't move on from one until you're completely done with the one before, including polish. You'll learn a LOT from polish, and you'll have something you can be VERY proud of (and can include in a portfolio). That's worth a lot.

RPG's are a bit too much to start with and for practice I think that a simple side scroller is a good start.

RPG's are a bit too much to start with and for practice I think that a simple side scroller is a good start.

That would definitely normally be the case, but isn't necessarily true when dealing with simpler purpose-specific software like RPG Maker. The advice to start small is still good however and can still be applied by starting out with single-room, single enemy levels, small combat prototypes, etc.

possibly wrecking any potential for story and plot and making a bad game.

Never worry about "what if i make a bad game". Do it for fun, and for yourself and enjoy it. If someone else thinks your game is bad, what does it matter, you wrote it for your own entertainment. If you think it's a bad game after you're finished, it's not the end of the world. Take a deep breath, sit back, get a pencil and paper and start on the sequel... which will be better than ever :)

Good luck!

Hello World!

Pong

(Crawl,walk,run etc)