Well, I'm not an android developer yet, per se, but I can give you a few pointers. First, it really depends on what you plan on developing to pick the right tools. There are a few that are essential no matter what you are trying to do, though.
First, do you have any programming experience? That will certainly help you out. These are not in any particular order. I don't have much time right now to really build a full guide, but I'm sure with some intuition you can figure it out.
Eclipse IDE (Development Environment, not necessary, but definitely a must if you plan on doing any coding.)
Download Link: (Eclipse Classic 4.2 is sufficient)
7zip (This is a utility that you can use to browse the archives of an .apk without decompiling. This is a great utility, especially for themers that are just replacing .png files.)
Android SDK (Rather than explaining, this one I'll just give you a link: )
Android Kitchen by Dsixda (This is a great tool for learning how to build a ROM, especially good at working off of someone else's base.
APKTool, APK Manager, or APK Multi-Tool (Essentially, they all do much the same thing. Good for compiling/decompiling apk's.
HashCalc (This tool is essentially a md5 sumchecker)
I can try and expand on this list in time. Also, I'm sure some other devs will be more than willing to give you advice. If you have any other questions regarding downloads, installation, or use, just ask here or hop in the chat, I'm in there pretty often, as are many other devs.
Edited to include download/informational links.
Edited by DCarrollUSMC, 24 July 2012 - 08:52 AM.