Falling off the meditation wagon is common. It happens to us all. The important thing is to not dwell on it too much and simply start again today.
1) If you have just missed a few days, then it's fine to pick it up from where you left off.
2) If you have missed more than two weeks, then I'd recommend one of the following:
a) If you are on Take10, Take15 or Take20, then start at the beginning of the particular programme you left off on. For example, if you last did Day 4 of Take15, start back with Day 1 of Take15.
b) If you are on a series pack, such as the Discovery Series, then simply return to the first day of the pack you were on. For example, if you last did Day 7 of Part 4, then simply return to Day 1 of Part 4 of the Discovery Series. There is no need to begin an entire series again if you have only missed a week or two.
3) If you have missed more than a month or so, then you can follow the same advice as above, but it's well worth doing all of Take10 again first, no matter where you are in the journey, just to get yourself back into the swing of things and to make sure it becomes part of your routine again.
By following this advice you can be sure that you will feel confident, clear and motivated when you begin again. It will also feel a lot more satisfying.