I lost 68 lbs over the course of a year by moderate changes in diet and exercise.
Clearly with diet, I suggest you don't want to make radical changes that you can live with over the long term. Yo-yoing, going up and down is actually bad for you as well.
I started by doing modest exercises - walking, biking, taking the stairs. Over time I increased them.
Diet wise, I replaced white pasta with whole wheat (more filling and more nutritious) and moderated the portion size. I did the same with bread - whole wheat bread or a rye bread is more nutriously dense, so you need/want less of it.
Probably the most important diet tip. EAT MORE VEGGIES. Whether its salads or soups or raw, eat more. Cut out starches like rice and potatoes and replace with more veggies. If you are eating veggies without butter or sauce, eat as much as you like. If they have sauce or butter, eat less, but eat them.
Get lots of sleep. Yes there are studies that show that weight loss efforts are enhanced by getting enough sleep.
Cut out the junk, replace with healty snacks. Fruit has natural sugars, but it also has vitamins that you need. Nuts in moderation are good snacks, hummus and raw veggies are easy and healthy. Crackers are healthier than crisps. Cheese in moderation is better than junk food (and protein helps you feel full). Moderate consumption of alcohol. Add more plain water to your diet.