1- STICK to the porgram it does work.
2- READ all the "success tools" on the mymedifast.com site- they are VITAL
3- plan in advance, do not let yourself get hungry on this plan.
4- Keep extra food with you at all times such as bars and puffs in case of an emergency.
5- do NOT skip meals, you may think skipping a meal here and there will help, trust me it doesn't.
6- it still takes time to lose on MF. Your first week will probably be your best week and then after that for women the average is usually 2-3 lbs while guys are better at hitting the 5 lbs per week average.
7- Week one is the hardest, make sure you drink TONS of water and also take advantage of the snack list (under success tools) because some of the snacks can help you survive (ie 2 pickles, 1 tbsp of pb, some broth, etc). And don't suffer through the headaches, TAKE SOMETHING for them
And remember- the closer you get to your MF goal the slower the loss- unfortunately that's how it is.
And the most important advice is don't get off plan! It's super hard to get back on (I speak from personal experience).
One more thing- if you do go off plan it's okay- no one is perfect, just keep trying.
Good luck! I'm doing MF it's great