I am also doing VLM and it's the first time for me,but not my first Marathon.
The main advice I would give is find a training plan you can easily stick to.They are generally 16 -18 weeks so you would need to start one in December.
Before that just start some light work ( a couple of miles twice a week) or go to park run (sorry cannot post link as doing this on my phone, just google it)
Even better if you fancy it join a Running Club plenty of advice and structured training
Good luck