If you are in the UK, get up, get out and vote!
That said, while I think voting is a duty incumbent upon all who enjoy the benefits of living as citizens and subjects in this sceptred isle, I do think there would be something to be said for ballot papers containing a “none of the above” option. I can understand that people might not want to support any of the candidates or feel that they don’t understand the policies well enough to offer a substantive opinion. Staying at home can be mistaken for apathy, so why not an option to express dissatisfaction without suggesting that perhaps you just can’t be bothered?
That said, there is an unwritten “none of the above” option; spoil your paper. Write something on it other than a single cross and it won’t count. You could scribble a quick sentence explaining why you can’t or don’t want to pick any of the candidates. At the moment there isn’t an intelligent way for collating the comments but it does express an active participation. The number of spoiled papers is counted and I think it would be much healthier for our democracy if there was a high turnout with a relatively large number of spoiled papers than a low count on both scores.
If nothing else, it would signal to the politicians that the nation is watching rather than letting them imagine that they can concentrate on people who will vote for them and ignoring everyone else.
Better still though is to cast a valid vote if you can decide but, please, get out and put something on the ballot paper that has been reserved for you.