The dreaded plateau

Patience.
Verify the accuracy of your logging.
Patience.
Take a maintenance break of a few days or even a week if you've been losing weight for a while.
Patience.
If you've lost a lot of weight, make sure your calorie goal is adjusted. MFP does it automatically for some, but for others, like me it doesn't: change your goal settings (for example your activity level and weight loss rate) and then change them back and your calorie goal should be updated to your lower weight.
And have I mentioned patience? 😉

I've never had a true plateau (6 weeks of no progress) although I have plenty of weight fluctuations, stalls and even upticks. Patience was always the answer, the scale always ended up going in the right direction.

if I appear to be at a real plateau - instead of simply not losing for a couple/three weeks, in my case usually due to my monthly cycle - I reduce my sodium for a day or two and eat my maintenance calories for a week.

One of those things, separately or in combination, usually prompts my body to ditch water weight. That's the only sort of 'plateau' I've experienced (over a year and from obese to mid-range healthy BMI).

Which of those 'dump the water' method works sort of depends whether my water weight is up due to stress from being at a deficit too long or I ate 900 billion mg of sodium over the past week. The second one's pretty rare but I do it occasionally. Doing both of them doesn't hurt anything, anyway, though, so I just do them both.