1. Getting the right running shoes is the main thing. Dont even think of doing anything else before you start training. You don't want to mess your legs up as you wont make the 100m mark.
2. Your diet is crucial whilst you train and the days before a race.
http://www.runnersworld.com/nutrition/the-right-way-to-carbo-load-before-a-race
3. Always warm up and down.
4. Make sure you rest a week before hand.
5. Get lots of sleep the night before.
6. If its a Saturday, book Monday off work. If it's a Sunday, book Monday Tuesday off.
I think from now until April is a huuuuge ask as your muscles need to build gradually to be able to last running that long which can take many moths (hence why people book it a year in advance). However, with the right shoes, diet and training program, (Depending on how fit you are now) it should be possible.
The Up and Running shop on Deansgate have free leaflets such as 'from 0 to 5k', '5 to 10k' 10k to half marathon' and '1/2 marathon to marathon'. Each have diary in which will be of great help.
Remember. It's not a race.