I wrote this piece on a basic tune that will get your rifle working very nicely. It is cheap to do and you aren't making any serious modifications so it is pretty safe for a beginner. It is what bigtoe01 (one of the 'serious' tuners on the forum) calls a 'spit and polish' tune. It will transform the feel of the rifle if you are going from an untouched out-of-the-box rifle or if the rifle has got a bit tired. Try it on a cheapie like a BSA Meteor or Gamo if you want to practice. The nastier the rifle the bigger the transformation...
It will make your rifle smooth, consistent and accurate if done right. You can then move on to buying a tuning kit e.g. V-Mach, Welsh Willy, Maccari, Vortek and try one of those. After that it is the realm of serious tuning and you will either have to buy a lathe or get friendly with someone who can operate one. There are several engineers who can make up parts for you on the BBS but obviously you will have to pay them for their services.
Couple of additions; I strongly recommend getting some good parallel-sided screwdriver bits, some good parallel punches and Allen keys, and also make yourself a spring-compressor or get a long sash-cramp and modify it appropriately. Even if your rifle has only a small amount of preload it makes life easier and safer. You will also need a chronograph to check the power of the gun afterwards.