Here’s some links to help you decide:
https://voteforpolicies.org.uk/ – Vote for Policies, not people. Find out the party you most align with, by choosing the policies you prefer.
http://www.theyworkforyou.com/ – Find out what your previous MP voted for
http://www.votenone.org.uk/protest_votes_count.html – A campaign to vote none as a protest.
http://www.bbc.co.uk/news/politics/constituencies – Find your Local Information
If you have the time look up your local Hustings, a chance to ask your local candidates some questions.
And sources: http://www.electoralcommission.org.uk/__data/assets/pdf_file/0012/87699/UKPE-doubtfuls-booklet.pdf
If you don’t like any of the candidates in your area, or want to ‘protest vote’, spoiling your ballot is much, much better than just not voting. Here’s some info.