Step 1: Find out what channels you want to watch. English-only, or international stuff?
Step 2a: If English only, get a sky subscription. This includes all your freesat channels. No new hardware required.
Step 2b: If international, try purchasing standard 80-100 cm dish + multi-LNB bracket, and some decent LNBs (e.g. Invertos) + DiSEqC switch. Also get any decent STB (e.g. TechnoMate) or similar to watch the channels through.
Step 2c: Get an 80 cm standard dish + a motor, and a decent STB box (again Technomate, but also Topfield, ClarkeTech, Vu; or even a DreamBox if you are so inclined).
Step 3: Mount dish+LNBs on exisitng mount, wire LNBs to DiSEQc switch, connect switch to existing cable, and connect STB to other end.
For more specific advice, post more specific needs