Coming down from 300 to 260 honestly was me just getting involved in cycling. It was something my family did together often and so they encouraged me to join them and I found I liked it a lot. After switching to a new job and moving, I was within biking distance and I started biking to work (although it was only 15 minutes, still kicked my butt). Around this time, I stopped smoking too.
The major weightloss came from starting Jim Stoppani's Shortcut to Shred. Something last March made me go to bodybuilding.com and look at their plans. I remember almost settling on a "beginner" routine but I saw the shortcut to shred one and it was labeled like advanced/expert. I watched the intro videos and decided to take it on. I nearly threw up every workout for the first two weeks but I stuck with it. Nowadays, I still do the same style of workout but I have modified the lifts a bit, just to add variety. I definitely recommend checking out Jim Stoppani - he's very inspirational and I do enjoy all of his different workouts and he's easily reachable on facebook.
As far as eating, I started using the shortcut to shred diet plan but ended up changing it quickly. In general, I went with .5g/lb of body weight for carbs and aimed to get about 180g of protein a day. I used myfitnesspal to track all of this (find me there as h4xit if you'd like). I brought my calories down from 2000 to 1600 as I continued to lose weight, and now I am at about 1800. With harder workouts, I found that I needed to eat more otherwise I would just end up being weak. I shifted to a mainly protein diet: eggs and every sort of meat were a majority of what I ate. I also start every morning with a berry/protein smoothie and have salad for lunch. I've added pistachios/almonds/cashews to my daily routine as well now.
Also having a workout partner really helped. /u/Stephanista really helped me stay motivated at the gym and together we've lost about the same amount of weight to this day (check out her progress post here. We kind of both motivate each other to stick with it and do so in a healthy, educated, and smart way.