Shimano Revo shifter does not shift I have recently bought a new bicycle and the left Shimano Revo shifter (3 speed) is not shifting, what can I do?
To really know what is wrong we need more information. But to give you some help:

If you don't know how to re-adjust the gear to shift correctly:
- Clean the derailleur (which pushes your chain to another gear).
- Push the cable back and forth a bit, and if possible, oil it a bit.
If this didn't work and you don't know how to adjust your gears to work correctly, bring it to a bicycle mechanic (such as me!). Because you can't do much more without disassembling the cable.

If you do know how to re-adjust the gear, this works better:
- Disassemble the cable.
- Clean the derailleur, and put some grease on the spring.
- Take out the inner cable, and spray a lot of oil in the outer cable
- Assemble the cable inside the outer cable. Check if the shifter works correctly by pulling the cable and shifting.
- Assemble it al again.

edit: it took me 2 edit's to correctly write 'inside'!