A dip in the pool can be a great way to improve your running. You don't necessarily need to know how to swim either. All you need is a pool and a kick board.
I've found that kick drills can be a great way to improve your running. It builds strength in your hips and can provide you with that extra umpth when tackling hills in races.
All you need to do start at end of the pool. Put your kick board in front of you like the video below and kick 25 yards to the other side. You can stop with a 15-30 second break before heading back. Repeat these for 30 minutes.
Spin classes can be a great way to break up the monotony of indoor training. You can find these classes at your local gym or a private spin studio. I prefer the private studio as they tend to be more fun. I get asked a lot about spinning during the winter. I lot of people are curious about spinning, but are apprehensive about it being too intense. Let me be the first to tell you, spinning is really only as intense as you make it. Essentially, you dictate the resistance on the bike. It's up to you to push yourself. So, if you're new to it. Don't worry about making it through class as you can dial back the resistance, but the only way you'll get better is if you keep it on or go harder in your next class. Another benefit of studios in our areas is they are private, lights are off, and it's not a race. Many studios are a sanctuary for your work out. Not a place that fosters competition. Spinning can help your running as not only do you keep fit, but your heart rate will be elevated like running.
I'm sure everyone reading this has there own ways to deal with running indoors. I keep things interesting with changing my runs up during the week. I like to do 1 speed work session during the week. Essentially, it consists of a 15 minute warm up at easy pace. Then I do 6-8 intervals of 800 meters at slightly above my 5K pace. I take a 400 meter rest between intervals and then do a short cool down afterwards. If you want to add speed during the offseason. This is the best way to do it. Another change of pace I do is week is I start the treadmill at a decent pace and then increase the speed slightly each half mile. I've found that adding these works to my treadmill routine spices things up from just logging miles away at the same pace.
I hope some of these sample workouts help if you are finding yourself in a rut or falling behind in your training. There's no exact science behind these workouts. They are just a sample of some things that have helped me with running and training.