First Half Marathon Done

Hi Guys

Wonder if anyone can give me some advice; I recently completed my first ever half marathon, in 2:39. Not a great time at all but I'd liek to improve my speed and wondered if anyone could give me some adivce.

I want to build up to a marathon, maybe Sep/Nov next year but at the moment i want to ask if its achieveable and realistic if I could train for a sub 2 hour half marathon?

Theres one in March which Id liek to enter for, but not sure of a few things, a) if its realistic to knock off 39+ minutes, b) how to I train for it or find a plan c) should I be concentrating on trainign for the marathon rather than the half?

Im 36, overweight by a few stone, so am hoping that would help if I shift some but would erlaly like some advice etc as Im itching to get started on a trainign schedule.

Ive seem some gereric sub 2 hour plans online but they seem unrealistic.

Thanks for the advice in advance.

Darren