First Im assuming your derailleur limits are set.

Could be slack in the cable if your shifts aren't moving the cable.
EDIT: For rear derailleur
Click the shifters into the hardest gear(smallest cog) each shift into an easier gear pulls the cable moving the derailleur
Disconnect the cable from the derailleur and give it a big tug with a pair of pliers.
At this point all slack should be gone from the line.
Then reattach the cable to the derailleur.

For the front derailleur:
Shift into small ring on shifter
remove cable, pull slack and attach snugly back to derailier.
Now when shifting to big ring, the cable should be taught enough to pull the derailleur up into the big ring.
The barrel adjust should allow you to fine adjust cable tension.

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