To help you out designing for specific devices, we have compiled a set of templates for Adobe illustrator.
Samsung, HTC, LG, Sony, Others
All of these uses 24/48 pixel icons
Websites, Web applications
Uses 8, 16, 24, 48, 64, 128, 256, 512px icons
Uses 62/62 pixel icons
How to setup illustrator for better icon designing with templates
The process/guides explained below are a work-in-progress. We're constantly refining the process and learning new tricks and experiment with different approaches, combinations, and tweak the grid.
You can use a 32 x 32 pixel grid but you don't have adhere exactly to the grid if, you feel like adhering to the grid to rigidly can hurt the aesthetic of the icon. So you can follow the grid more as a guide than a set rule. Going forward, you could be using two grids: 24 x 24 for Android, and 30 x 30 for iOS.
There are some odd ball icons that don't adhere to the grid at all. In some cases you can abandon the grid because the icons needed to be what they are and the grid just didn't work with the designs. In other cases the icons can be slightly larger than the grid for aesthetic reasons.
You can use three palettes for almost every icon: Pathfinder, Stroke, and Transform. Pathfinder is the most heavily used for joining and knocking out shapes. Use stroke in conjunction with the menu Object > Path > Outline Path. This allows you to quickly outline a shape, apply a stroke, outline the stroke in cases where you need to convert an outline to a vector area rather than a stroke. Transform contains the "Align to Pixel Grid" feature. This is especially useful for making icons pixel perfect, along with the View > Snap To Grid option. But be careful with this one. Using "Align to Pixel Grid" on a curved vector can give you funky results.
Snap to Point - Snap to Grid - Smart Guides you should keep Snap to Point enabled at all times. You can alternate between Smart Guides and Snap to Grid. The latter two can confuse one another because illustrator can't figure out which one you want to apply when a point is close to an object with a similarly aligned point and close to a grid intersection or line.
You should try, as much as possible, to work with line weights that are multiples of two because the lines seem to scale better, both larger and smaller (it's easy math). But visually you should use a combination of 2 pixel lines and 3 pixel lines. At 100% scale, 3 pixel lines render clearly provided they are pixel perfect.