One of the strongest predictors of maintenance success is physical activity. Weight lost through diet alone will generally decrease lean body mass, resulting in a lower total daily energy expenditure (TDEE or calories burned). People who reach goal weight without exercise will be unlikely to maintain because they do not have the lean bodymass to keep up their metabolism at a reasonable calorie level.
However, it is not wise to jump full throttle into an intense exercise regimen (like in the disclaimer that you should always see your doctor to get cleared for increased physical activity.) Besides the familiar cautions against soreness and injury, too much activity too soon will raise your TDEE too fast, resulting in increased hunger and the likelihood of overeating. Over exercising can also cause transitory water weight gain. In the STOP Regain study new maintainers were instructed to build up their level of physical activity gradually.
Action step: evaluate your current level of physical activity and find ways to increase it gradually each week — five additional minutes of moderate to intense activity or ten minutes of walking per day. Increase this each week unless you already do 35-60 minutes a day (depending on intensity).