Register as an Overseas Voter
Step One: Register to Vote
This can be done online at www.gov.uk/register-to-vote.
There is also a paper method which is explained on that site.
After registering the details on-line, these are sent through to the local authority for the actual registering. The authority may have questions after checking your details, particularly if you have never registered to vote before in the UK.
Step Two: Choose Postal Vote or Proxy Vote Option
If Choose to Register a Postal Vote
This can be done at www.gov.uk/register-to-vote
But be aware that in many or most countries there is no certainty mail will arrive in time for you to complete a postal vote and ensure it is back to the returning officer for your locality in time.
If Choose a Proxy Vote
This can also be completed at www.gov.uk/register-to-vote
Note The Proxy needs to be a registered voter for the same election as the person he is registered for but can live anywhere in the United Kingdom
Step Three: Proxy to Register their Consent
The Proxy Voter who you nominate in Step Two will be contacted by the local authority handling your registration in order to register his consent to be the Proxy and to confirm his/her details.
Note the Proxy can choose to vote in person or to vote by Post (the Postal system can be relied upon in the UK to perform its role in time).