Be consistent in what you choose to do and stick with this. Make one or two changes in your routine and stick with this consistently. These changes could include drinking more water, walking on the treadmill, cutting out fatty foods from your diet. Whatever it may be, the key is being consistent in your approach.
Follow an effective exercise routine. This could be strength training (about 20 mins), interval training (for example walk for 2 mins and run for 2 mins and alternate again) or cardio or aerobic exercise (usually 60 mins).
Set yourself realistic goals. The goals you set need to be achievable otherwise you will feel demotivated and may not continue. Focus on increasing the healthy behaviours.
Make use of a buddy system. If you are not feeling motivated, make sure you have a friend meet you to motivate you. Committing to a time and another person will make you be more accountable and more likely to follow through.
Have fun. Do exercise that you enjoy! If you enjoy being in the outdoors, find a routine that allows you to be in this environment. If you enjoy quiet choose yoga. Find what works for you.