A good start would be going to RunITDirect and buying a new NTE5 line box -
NTE5 Master Socket - With Openreach&#8482 Logo

If you don't have a good backbox, get one of these too -
22mm Back Box

They are easy to fix, screw the backbox to the wall, feed the cable through one of the knock-outs and connect the orange and white wires to the A and B screw terminals. Screw on the main plate and screw the faceplate on to it, and that is it. If you have extensions it would pay to get a filtered faceplate, which replaces the existing faceplate.
BT NTE-2005 ADSL Faceplate for NTE5, 6 Way Version

Total cost about 20 or pay BTO about 150 to do it for you.