Cutting down blinds (Specifically metal frame - not the blind itself)
The hand tool for cutting metal is called a hacksaw. For neater cuts, select a blade with fine (narrowly spaced) teeth.

There are many kinds of hacksaws available, but for this use you'd want a traditional one. There are mini hacksaws which might be cheaper but a larger one will make the work faster and the cuts smoother. 

After you cut, you can smooth the edges using some sandpaper or a medium/fine sanding sponge. Be careful as you handle the piece because cut metal edges can be sharp.