NEW YEAR;RESOLUTION. HELP?!

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Okay, its a new year. So i figure its a good time to start fresh & lose some weight. I am 16 years old. I am 175lbs. I am no longer happy with myself. I've let it get too far. Anywho, i go wednesday to get a membership at an all girls gym up the road,i was wondering if anyone had any good tips to keep me motivated?& other tips on losing weight.
THANKS!<3