Shimano's Deore shifters are very popular mountain bike style shifters known for their ease of adjustment, dependability, and shifting accuracy. The shifters come standard on many mountain bicycle made by companies like Trek, Specialized, and Jamis. They will only, however, work correctly if they are kept in good adjustment and repair. If your Deore shifters aren't working, fix them at home and save time and money over taking the bike to your local bike shop.
Loosen the cable stop of both the front and rear derailleur using a combination or hex wrench (depending on your derailleurs). This should allow the cables to slid through the cable housing freely. Turn the barrel adjuster of each shifter lever clockwise until it stops to set the adjusters back to "zero."
Hold the cable of the front derailleur taught with needle-nose pliers or cable grips while you tighten the front derailleur cable stop. Make certain the cable won't slip by pressing the shifter lever up and down a few times.
Hold the cable of the rear derailleur taught with needle-nose pliers or cable grips. Tighten the cable stop using a hex or combination wrench so that the cable doesn't slide through.
Take the bike for a test ride and shift through all the gears. While you are riding, adjust the shifter cables by turning the barrel adjuster of each shifter clockwise (if the bike shifts more than one gear at a time) or counter-clockwise (if the bike misses shifts or doesn't shift at all).
Make any necessary final adjustments when you finish your test ride. Make certain any bolt or cable stop you loosened while working is now tight, and get ready for a nice long ride.