How to adjust rear derailleur

Hi,
Just went out for a first ride for a few months and I am having problems with shifting down on my rear derailleur. It has 7 cogs. I have a control that if i press it hard it shifts down 3 gears at a time. What's happening now is that i have to push it nearly all the way forwards to change even 1 gear down, and it doesn't shift 3 at a time any more.

I guess it's something quite simple with the cable, and I have googled an incredible amount of advice out there, but someone here will hopefully know a simple "turn this screw" or point me to a good easy to follow website so I can adjust my gears easily.

The front derailleur is fine, and I can change up gears 1-7 without problem.
many thanks
Rob

You seem to know this already, but a rear derailleur's mechanism is just the cable pulling when going from small-to-large sprocket and cable releasing (allowing spring to restore) when going the other way (large-to-small). Your description of the problem was not entirely clear, but are you having problems when going from large-to-small sprockets i.e. when the cable is releasing/spring is pulling chain outwards?

I am not a repair expert, but maybe there is a problem with the shift lever, which is now only releasing enough cable to allow a shift to the adjacent gear. Or, maybe there is friction somewhere (in cable, in derailleur, etc) causing the spring to have problems. Some time back, I had somewhat similar rear shifiting issues on a neglected bike that developed some rust. I was able to fix it by changing the cables and applying oil to get the derailleur to stop sticking at the hinges.

Try posting the make and model of your set up. Knowledgeable folks may have something more to say.

Replace (or remove and clean) your cables. Sounds like something could be sticking, failing that something could be worn in the shifter mechinism... Cables first though...