Do less than you can.
If you can meditate for 25 minutes, meditate for 23. If you can meditate for 10 minutes, meditate for seven. If you can meditate for three minutes, meditate for 2 1/2.
This advice is designed to help you overcome one of the most unhelpful human traits of excessive expectation. This is a thing known as impact bias. You can read about impact bias on Wikipedia here.
Although we are looking for an overall improvement in our practices, the more we need, want, or expect a particular meditation to deliver the desired outcome, the more elusive it will be. This is the same as needing to get to sleep getting in the way of our sleep. The more we need to sleep, the more elusive it becomes. The more we expect from meditation, the less likely we shall achieve it.