Persuade a plurality of voters in each of a majority of constituencies to vote for candidates other than those of the Labour Party, preferably by ensuring that a plurality or majority of the seats are won by a single party other than the Labour Party. The best way of doing this is by voting where posssible for the OMRLP.
Convince people that there exist a real reason to vote....Both the labour and tory party members have shown themselves to be snout deep in the trough as far as corruption goes and both parties policies have graviated towards the bland and ineffectual so as to try and not to alienate anyone rather than actually excite anyone. The Liberal party may be a remote possibility but most voters would still see them as a distant third and given all that why bother....It's really not going to make a big difference one way or other as one bunch of cheating self serving liars or the other is going to get in anyway.
sft42 - I would not consider the Liberal Party to be even a remote possibility. They only had 14 candidates at the last election and no MPs. The party membership and organisational strength has gone down considerably since then.
I have given up voting, simply because I dont want to be responsible for the next goverment taking me for a ride and robbing me blind, these days they are each as bad as each other, its not apathy, I think you can make more of a statement by not voting!!!