This is a tricky situation.
How do you approach the training between closely scheduled races?
For example, lets say you have two events that are 2-4 weeks apart and wish to attend both. Maybe a half marathon and a full marathon. Here's the process:
Relax and Recover
Such a short amount of time is not adequate for you to gain any more fitness from training.
A general rule is true recovery takes a single day for every mile at race pace. This is why elites only do 2-3 full marathons yearly, it takes so long to recover and begin training again!
"Better to go into the race 10% under-trained than 1% overtrained"
Not that you will loose any significant fitness between the races. In fact, the first race will give your body something to adapt to!
That half marathon will take two weeks for full recovery to occur. At that point, you may only have a couple days or a couple weeks until the second event! The best you can do is allow this recovery to take place as best you can. The worst thing you can do is start difficult training back up too quickly. Any overly stimulating workouts will only build upon your fatigue and delay recovery.
If you have two races in close succession, here is an outline of how to handle the time between.
2-4 days post race
Take these days completely off, to prioritize recovery. Depending on the length of the race, anywhere from two to four days. Go for a hike (such as the header image) or some short bike rides.
4-14 days post race
Slowly transition back into running. Keep things light and easy. Remember no matter how good you feel, you're not fully recovered. Avoid long runs or any intensity.
1 to 2 weeks prior to the next event
You're now basically into another taper. Keep the volume lower and do a couple sessions of speedwork and add some strides into your easy runs. Remember, nothing should leave you fatigued though. It takes about two weeks for your body to reap the benefits of a key workout, and you simply won't have enough time for that here. That does mean the first race will provide some added fitness for the second event.
Have you done two workouts in short succession before? What did you do between them, and how well did it work?