Exactly as cougie says- you are probably at high risk of injurung yourself if you are quite fit generally, but not used to running regularly- if you ramp up the mileage quickly, you will probably suffer an overuse injury to some part of your legs after about 6 weeks.
Probably the most important thing, as you are suddenly doing more mileage, is to do it all as slow as you can- don't do any speed stuff until you are really used to the regular runs, and don't be afraid to walk /run some of the longer runs, if it stops you getting injured.
Good luck....you never know, you may be one of the lucky ones that gets away with a non- textbook trainig approach, but be prepared to stop and get help if you feel an injury coming on.