Christian Cunningham has shared a useful guide to dealing with normal maps.
First of all, there is no perfect way to bake a model, but there are some simple rules that can get you close to perfection. The written tutorial features 7 tricks to help you figure out the process.
Here are the guidelines:
- Only have hard edges on 90 degree edges and higher, everything else must be soft
- Wherever you have hard edges, you must have UV splits as well
- Provide ample padding on your UVs so there is no bleeding
- Before exporting your cage (if you are using floaters) make sure that the normals of the faces are flat
- Even if there is a bevel, where you want a hard edge to appear, smooth it on your low poly. Let your high poly create that crisp edge
- You have to do all of this and continue to worry about correct YV layout and hiding your seams.
- Export using .obj
You can get a free copy of the guide with more comments here.