First of all,
dAwjbNS says ....In general: It's mostly a matter of learning from experience. Try not to touch them

... and remember that they knock your bombs around, so if you want to freeze a fruit, you have to do it when the razor isn't around ... and if you want to freeze a razor, you have to place the bomb much further away than usual so it won't be pushed away.

Protip: The razor on 46.2 (Cadomax .3) can kill you if you stand on the side next to a teleporter, no matter how far away you think you are. Speed is key on this level. Wait for the items to appear, then get in and get out before it traps you somehow.
The razors on .3 (Cx .4) can almost always be avoided by just hugging the wall, or waiting for it to pass before proceeding.
On .4 (Cx .5), wait for the first two Bombinos to come up and kill them before you enter, so they aren't in your way. Always be alert of the razors on both sides of the teleporter as you're entering one. This level mainly just takes a lot of practice to get used to. Be patient, above all.
Phew. Hope this helps.
