If there's one thing I can't endure, it's working out indoors. For me, the enjoyment in cycling isn't just the essence of training. It's about being outside, seeing different roads and landscapes, and actual racing. I always prefer playing sports to "working out," so riding the trainer in the winter has always been the pinnacle of drudgery. I would rather ride outside in 33 degrees and rain than strap myself to a machine indoors.
At the same time, if you work long hours or live in a winter climate with cold, short days and dangerous road conditions, riding the trainer is probably a necessary part of your early season preparation, and one you'll need to make the best of. It doesn't have to be all pain and misery, though, if you take the right approach.
The essence of my indoor training strategy is to view the trainer the same way you would a machine of any kind in the gym. You get on, you do your efforts, and you get off. Don't view your time on the trainer as a "ride." The first thing you should change from the approach you'd take to an outdoor ride is being concerned about your duration for the day. Focus on the work planned, and get those intervals done.
For example, if you planned a 3-hour ride, with 60 minutes of tempo intervals, translating that ride to for indoor training would see you disregard the duration goal and focus on the intervals. Take 15 minutes to warm up, do the work in 2 30-minute intervals with 5-10 minutes of recovery, cool down, and climb off. You can get the majority of the value of that 3 hour ride done in 90 minites or less.
Another key to making indoor work bearable is that the recovery can come on or off the trainer. Get off between efforts, get some water, stretch--just like you would between sets of lifting in the gym. When you're ready, get back on, spin for a few minutes to get comfortable, and do your next interval. This approach is also similar to what a track workout would be, where it's not so much about "going for a ride," as it is getting all your work done.
Another tactic is to mix up what you do. Some clients prefer to warm up and cool down on the rollers, but do their interval work on the trainer. You can even mix indoor and outdoor work into a single workout. If you don't like to ride after dark or perhaps are commuting home and have time to do most of your work, you might come in and finish your intervals on the trainer in the safety of your own living room. You can meet for indoor "group rides" and try to get a few people together to do their workouts at the same place in order to pass the time more enjoyably. And if you can't do all the training in one go, you can even split the workout up into a morning and evening session.
It's also important to consider having the right tool for the job. Rollers or trainer? Wind, fluid, magnetic, or direct drive? Rollers are useful for developing a smooth pedal stroke and improving balance on the bike. There's very little resistance, however, and you might be limited in terms of the intensity of the work you can do on them. Early in the year when your work is primarily aerobic, you'll find you can do most of it on the rollers without difficulty. Of course, you have to pay attention, which has its pros and cons. It takes considerable concentration if it's not second nature, and there's nothing worse than interrupting an interval by falling on the floor. Sprinting on the rollers is always a fun challenge, and while you might not achieve maximum wattage, you can certainly work on leg speed and timing. If your skills are good, you can show off by getting out of the saddle, riding no-handed, or even taking a sweaty jersey or T-shirt off while you ride. If you really enjoy doing your indoor work on the rollers, you can buy brands that use small diameter rollers or add-on resistance units to increase the difficulty. A trainer will offer more stability and control over your effort, but takes away the natural road feel you get on the rollers. The advantage here is in being able to do precise, consistent efforts with no distractions. Certainly, the type of trainer you have can make a difference. A windtrainer uses a small fan that simulates wind resistance outdoors, and gets exponentially harder the faster you go. A fluid trainer achieves the same result with a sealed hydro system that's considerably quieter. A magnetic trainer is different in that the resistance increases linearly as you go harder; it doesn't go up quite as fast, but allows for more control over the resistance itself by allowing you to change the settings. Some trainers can measure wattage, or even include an interactive video display that can make things truly interesting.These days, with the advent of direct-drive training and indoor simulation software like Zwift, indoor training has seen a real revolution. With a direct-drive, flywheel based trainer, momentum is stored in the flywheel and that energy is carried over through the natural dead spots over the top and bottom of your pedal stroke, recreating the sensation of pedaling outdoors with your own bodyweight against wind and rolling resistance. It allows for less adaptation time, and the ability to make similar power to what you'd see outside. Add a "smart" trainer function to that, and connection to a virtual reality simulator like Zwift , and you can really transform your indoor time with terrain changes, group rides, and even training races. Zwift plus a smart, direct-drive trainer makes indoor training more tolerable, and makes completing work volumes similar what you could do outside more possible.
Whatever trainer you use and approach you take, the absolute most important rule is that the room has to be cold, unless you are specifically trying to do hot weather adapation. Often people see a 10% reduction in power at the same heart rate response. This is due primarily to the different pedal stroke requirements of most training (again, mitigated by a direct-drive trainer) and maybe more importantly, because of cooling requirements from working out in a hot room. My rule is, if you're sweating, it's too hot. If you're sweating, that's power you're not making. The windows should be open, the fan should be on, and you should need a long sleeve jersey when you first start riding. Take things off for your intervals to control your personal temperature, and keep a towel handy.
While I've had clients who had no problem putting in four-hour rides indoors and actually enjoy the work, I think for most of us riding indoors is a chore. With this approach, you can not only make your indoor training time bearable, you can hopefully use it to improve your fitness and prepare yourself for the season outside to come, or make the best of training days during the season where work or weather keep you indoors.