You can't boost the signal, but often there are things you can do to improve it. Quite a lot of problems with broadband are caused by poor extension wiring. Before broadband came along, it didn't really matter how untidy the wiring was, but broadband changes all that. Broadband uses the same frequencies as AM (Medium Wave) radio, and if you have a lot of extension wiring in your house, it will act as an aerial, and it will pull in a lot of signals that will interfere with the broadband signal.
If you have an NTE-5 type phone socket (see
http://en.wikipedia.org/wiki/British_telephone_sockets for a picture of one) it will have a removable front plate that should disconnect all the extension wiring when the front plate is removed (if it is installed correctly), and when the front plate is off, there is a 'test socket' that you can plug a phone or broadband router into for testing purposes. What you should do is to note the connection speed when the router is connected normally, and then remove the NTE-5 front plate and plug the router directly into the socket revealed under the plate, and then note the connection speed again. If you see an improvement in speed, then the extension wiring is affecting your speeds. The best thing to do if this is happening is to buy an iPlate, or a filtered faceplate. The Wiki page I linked to shows how to fit an iPlate, and the filtered faceplate replaces the removable faceplate on the NTE-5. It's vital that if you use a filtered faceplate, you connect your router to the ADSL output of the plate with no long wiring runs. The other advantage of the filtered faceplate is that you do not need separate filters connected to your phones - they are merely directly connected to the PHONE output of the filtered faceplate.
If doing the above doesn't improve things, then it's not your wiring. Try dialling 17070 (UK only) and then select 2 for a 'quiet line test'. You should not be hearing much in the way of clicks, pops or hissing noises. If you are getting a lot of these, then you should report it to your phone company as a voice fault (not a broadband fault).