It's that time of year again - if you are training to run an April Marathon, you'll either need to start training soon, or your training should be well underway. A good training program lasts about 18 weeks.
Which marathon do you want to run? Boston is probably the most popular. Off the top of my head I know the Big Sur marathon in CA is also in April, and so is Vienna.
Do you want to run your first marathon? Now is as good a time as anyway. Pick one, and then choose a training program that makes sense for your fitness level. This is the one I chose when I ran my first marathon:
I used the novice plan.