A mesomorph is born with a particular body type, inherited from the most dominant hits you've picked up from your family.
If you tend to put on fat somewhat less than you put on muscle, you are probably a mesomorph. This somatotype is known to be well proportioned, strong and naturally athletic.
An overweight mesomorph woman will still have an enviable waist to hips ration, with a classic hourglass shape. When you lose fat and get fit, you will still have great breasts in proportion to your waist and hips.
An overweight mesomorph man will look less flabby and unfit than his endomorph or even ectomorph counterpart because those wide shoulders tapering to a proportionately narrow waist will camouflage a lot of stored cream donuts or beer.
Being a mesomorph, you have inherited aifted body shape. If you are prepared to put in reasonable diet and exercise effort, your body will reward you with lean or mass muscle tone that is easily maintained once achieved. Your body will thrive on a clean, healthy diet.
Your metabolism is naturally very efficient and your bone structure is balanced.
What more could you ask for?
Probably 3 things, mostly
Divide your overall goal into ultimate goal (year / s), medium term goal (months) and short term goal (weeks). Keep monitoring your progress toward each aspect of your goal and be firm with but forgiving of yourself.
A reason to succeed
This has to be a reason that drives you, focuses you, forces you to make the effort. Not a wimpy little platitude like "I really should try to lose some weight", but something like "I am no longer prepared to be overweight, unfit and unhealthy." The new me starts today "
Well, that particular one worked for me, even though I'm just an inferior pear shaped endomorph. (Mind you, thanks to a bit of regular weight training, I now have the shoulders of a mesomorph).
A challenging, but achievable diet and exercise program will allow you to reach your goal in its entity. You are going to have to do some research to find the plan that will work for you. Go ahead and get yourself as informed as possible before you start.
I guess one thing in particular can hamper the mesomorph in their quest to lose fat and get fit.
A mesomorph does tend to look good wherever fit and toned or somewhat overweight, so your motivation to lose fat and get fit may just not be strong enough. But unless you make the most of the great body type you have been born with, you will never achieve your full potential in respect to health, fitness and appearance.
Casting besides the great advantage of being born a mesomorph would be such a shame. A missed opportunity. If you treat your body with focused attention, rather than neglect, you are going to look and (more importantly) feel absolutely fantastic.
Go for it. Be the best you can be (you have a head start on the rest of us!)