My method is to tackle the hard stuff right off the bat.
I started with Editing the Title Screen. D-Trough's NTME is a Must-have tool for rom hacking. I would start with Just getting the picture to show up correctly, then work on getting your Color Scheme. This way you have a good solid rom to work with, without worrying about corruption Later on in the rom.
They I would jump into scripting, scripting is extremely bothersome, It's not that it's hard. It's just very Repetitive and the slightest mistake can ruin the entire script into going back into debug.
Mapping is without a doubt the easiest to learn, tile insertion can be a pain, but mappers are easy to come by. Scripters are the hard one's to find.
My Advice, Learn the hardest parts, that makes you the guy in charge. You'll need more than just basic ideas, you'll need a whole storyline. Otherwise, how can you tell someone what to work on, if you have no idea what's next?