The state of the UK economy and the amount of government debt is the main reason the pound has fallen in recent weeks. The recovery from recession has been very feeble, and the amount of debt is growing at a faster than expected rate. With the general election approaching, recent polls are suggesting the possiblility of a hung parliament, which would be perceived as weak and less able to tackle the problem decisively.
Meanwhile the Bank of England seems to want the pound to drop to stimulate the economy. Add that to the fact that the euro has been weak against the dollar because of Greece, the pound has been dragged down with that too.
I personally think the eurozone's problems are worse than ours, but I'm probably in the minority.
Things that might make the pound go up would be an upward revision to the economic recovery figures or an increase in the tory lead in the polls.
It's very hard to advise what to do regarding timing - last year the pound dropped and at the time it all seemed very gloomy, but it recovered above 1.60 for a while, so you can never tell. If I say I'm pessimistic and you should do it now and it goes up I'll look like an idiot!