Hello!
It is always good to get into proper shape and start afresh and be very regular.
Physical exercise is a continuous method to stay fit and I would suggest you to be regular and feel motivated and continue for your lifetime to have a healthy life and maintain a BMI of 25.
Plan a balanced diet with the help of a dietician depending on your age and weight.
Start cardio as in running, jogging, skipping, walking, cross trainer, treadmill, swimming, skiing, cycling or any sport for around 45 minutes every day.
You can start some weights initially and start doing some mild exercises for 15 minutes everyday, follow up with a Physical trainer.
Take care!