Expect a little boredom now and then--we all experience it. The way I get around my boredom is to race.
Racing adds a dimension to running that a regular runner who is always on his own can't experience. Almost everybody who races would tell non-racers they're missing out, that this is what it's all about.
Fitness and health are running's great bonuses, but racing adds excitement that's hard to get elsewhere in your life. You can test your very limits. You can discover things about yourself that your regular life would never have revealed to you. You can be your own hero -- it's hard to do that on a daily training run.
And you don't have to become a hardcore racer to get these benefits. One of the best ways to beat boredom is to run with others. If you usually run three miles a day, why not run at your normal pace, but in an organized 5K race? See what it's like, and if this is a dimension of running that you want to include in your program.
You're likely to meet other people of your level of fitness, and maybe meet some potential running partners. A good running partner can go far to relieve some of the tedium.
Racing is also a big help because it encourages you to develop a seasonal approach toward your running. For example, I run about 25 races a year. My last races for the year are usually in November, and by then I'm ready to back off and change the emphasis of my running.
Throughout December and January, I pretty much do steady mileage -- going out and running moderately, like most beginners. By the time these two months are over, I'm eager to introduce more variety in my running, and I start racing and doing some harder training to prepare for the spring racing season.
Come summer, I back off a bit in my mileage and run mostly shorter races, such as 5Ks, so the heat doesn't drain me too much. As the weather cools, I increase mileage and prepare for 10Ks and half-marathons.
After all that, I look forward to a low-key approach, and I start the cycle again with my relaxed running in December.
Sure, there are still days within each season in which I might be bored, but by changing the emphasis in my running throughout the year, I'm able to stay very interested in it most of the time.
Finally, one of the best motivators I know is injury. There's nothing like having something taken away from you to make you realize how much you love it.
There are many great things in my life, but if I can't have the buttress that running provides, other things lose some of their luster. If you find that you're taking your running for granted, think what your life would be like without it.