Don't get a scale, don't post any pictures on Facebook(until you achieve your goal), don't overwhelm yourself too much too fast and be conscious of EVERYTHING you put in your body. You can count calories and after a while, you will just know how much you ate for that day without having to count calories. DO NOT drink pop, diet or otherwise. Water will be your new best friend if you're biking to lose weight, you'll eventually learn to love water.
Start slow at first, try to ride at least 2 miles for the first few days to get a feel for it(Using 2 miles but im not sure how much you weight, etc... so if 2 miles is too hard set the bar a little lower), that way you'll get a good understanding of how miserable this life change is going to be for you....for a while. You're going to want to quit every single time you ride at first but I assure you, eventually, you will crave the feeling of pushing your body as it was intended to be pushed. Every time you want to turn back because your ass hurts, your tummy hurts, someone beeped at you, your legs are tired just know you're essentially giving up on your own happiness and you will continue to beat yourself up every time you look in the mirror and realize that you're going to be stuck in that body until you die because you gave up, not for any major reason either, you basically let your doubts and insecurities beat you.
I can't stress this enough, you're going to fucking hate it for a while but once you start seeing a noticeable difference in your weight and that you're actually progressing, you will feel amazing both mentally and physically. The diet is key though, that's probably the hardest part. Just don't think because you rode 10 miles you can stop at McDonalds afterwards. Remove all that shit, forever. You won't regret it. And again, throw the fucking scale in the trash. When you look in the mirror and you're happy with the body you're in, THEN you can look at the scale. Until then, it's far too detrimental mentally when you're trying to lose weight.
Good luck and welcome to the fucking grind.