If you don't know who to vote for, use a website to help you decide (iSideWith, Vote For Policies, Vote Match - Google will help you). Don't choose a party or personality because of what your friend or the media say. Make your own informed opinion, don't join a bandwagon.
If you are still undecided, or believe none of the MPs are fit to run the country, write 'none' or 'no confidence' diagonally over the selection side of the ballot (don't leave it blank).
If you are missing your ballot, don't worry, as long as you are registered, you can still vote, just take ID.
If you don't have the time, remember you can vote between 7am and 10pm (last time for queue entry).
If you are unsure if you are registered, check using Noodle.co.uk to see if you are (and get a free credit report).
If you don't have the effort or are apathetic, remember that many countries don't have the freedom of choice, and our country historically hasn't always been equal for voting rights. It is a privilege.
Make your vote and make it count. As a qualified citizen and member of the UK, this is one easy step to making a difference to the future of your country, and ultimately, your life too.