Almost a million people, mostly students, were dropped from the electoral register due to a convenient policy change by the tory government as students are more likely to vote labour/green. See articles here and here. So please make sure you are actually registered to vote by calling your local office!
Now I know it seems complicated to vote from overseas but it's actually pretty simple. You can register to vote by proxy (getting a family member to vote for you) or by post. Given that it isn't long until the election, and post takes so long to reach home, voting by proxy is probably the best option for an expat.
Here is the link to get the relevant forms.
My advice would be to check where you are registered, ring them by putting credit on your Skype account, or go on the website and enter your details. Or if you are sure you are reigstered you have to register as an overseas voter here first by putting in the UK address you are currently registered to, then print off the proxy form and send it quickly via DHL or similar fast courier to your local authority and then obviously tell your family member who you wish to vote for.
Here are some useful links to give you an idea of the parties' policies. Might I suggest that people think about those less fortunate, rather than benefits to the already rich, and the risks that having another Tory term might bring to our education system, our unique and wonderful NHS and the values our society is clinging onto which are likely to be destroyed. Don't mean to persuade but I don't think my political stance is a secret to anyone who reads my blog!
Overview of all main parties
Labour Key Issues