Tips for manually decimating in Blender
Deleting Edge Loops
Use quads when modeling! We get nice things like edge loops
To select an edge loop, select an edge,
Ctrl-E->Edge Loop. We can then delete edge loop (Space, type it out) and use that to decimate parts of the mesh!
This helps create lower poly characters from higher poly ones, instead of having to re-model the character.
Alt-M to merge vertices, which can be used to squash triangles, or reduce polycount.
Be careful – it’s best if the model always contains only quads and very few triangles.