Welcome and thanks for choosing this 12 week training plan. This plan is designed to provide the structure and guidance necessary to build your aerobic capacity and endurance, muscular endurance and strength, and overall pedaling proficiency, as well as incorporating some good intensity. The language of the workouts are written in clear and common terminology centered around your individual Heart Rate (HR) and Power zones (PW). The 12 weeks are structured around a few full blocks of training which are then followed by a recovery week so that your body can recuperate and adapt to the workloads. Each week also includes 2 days of core strengthening and stretching yoga as cross training. This plan would best be applied at the beginning of a training phase or as structure for post racing season training. A large portion of the riding is concentrated on Zone 2 or Aerobic Endurance Training Zone. These types of workouts are specifically designed to build the bloodflow capacity and train the buffering of metabolic waste products.
For a more detailed look at this: http://home.trainingpeaks.com/blog/article/what-is-lactate-and-lactate-threshold

With that said, one of the most important things is to train yourself to ride easy. A successful day out on an easy or "Active Recovery Ride" will see your average watts at roughly half of what your current threshold power is set at. Similarly, a long Zone 2 ride should have your average wattage around 60-65% of your threshold. Some tips and techniques for keeping your intensity lower are as follows;
1) Anticipate your gearing when the terrain and gradient changes. As a hill pitches up, shift before you are forced to ride hard just to turn over the larger gear.
2) Do not accelerate hard from stops or lights. Often you will naturally sprint a little to get back up to cruising speed, try and avoid this. These rides are about the correct intensity rather than speed, so take your time accelerating.
3) Leave your ego at home. It is easier said than done sometimes but do not get caught up feeling like you have something to prove against other riders out there. Let elderly people on cruiser bikes pass you on your easy days and you will be the better for it.
4) Go slow to go fast. If you ever get a chance to ride with a high level competitor on one of their easy or chill days, do it! You will find almost categorically that the people who are the fastest on race day are the ones that know how to go the slowest on recovery days.

Thanks again for choosing this plan and happy riding to you!