I was asked this question in a comment this week and thought perhaps it deserved a post of it's own, then anyone else can throw in the 2 cents worth on what works for them.
To answer how I stay motivated I should probably address first what motivates me to practice and then consider how I manage to keep that up.
Motivation changes of course with the practice and over time.
I decided to number these for reference but they are in no particular order.
1. In the beginning I wanted to practice some yoga and deal with some anger issues and perhaps some stress after being burgled, that was the first motivation to practice
2. I became attracted to Ashtanga and was motivated by the challenge of the poses. I saw some videos and thought, cool, I want be able to do that.
3. As I started to practice I began to lose a little weight, Ashtanga seemed to be a way that I could get fitter and healthier. This became a major motivational factor that lasted for a couple of years. Now I seem to have leveled out and it's more a case of staying fit and healthy for the practice itself.
4. After a few months the Jump back became a bit of an obsession, you might have noticed. That was a strong source of motivation for a long time, and still is, lots of different kinds of jump backs and jump through's.
5. Poses that I thought I'd never achieve began to become achievable which made others seem possible until everything seemed to be possible (up to Advanced B at least). The practice is inherently motivating in this way.
6. I started to blog and that became a motivating factor. It was a place I could reflect on my practice, somewhere I could see progress happening. I started it to share information on the jump back, it motivated me even more to achieve that.
7. For a long time though I never really expected this blog to be read by anyone so it was really just for me. I remember when I would get maybe 20-30 visits a day, now it's between 150-228 (Wednesday was a record) depending on whether I'd posted that day. I've had a lot of comments and emails telling me the blog has been helpful, encouraging, even inspiring and that is highly motivating because the blog and the practice became so linked.
8. As I've progressed, I've been told again and again that sustaining a home practice is particularly hard, that having managed to sustain it thus far, feeds back into motivating me to continue practicing.
9. Being told I shouldn't do something....highly motivating, thank you everyone who's told me that, don't stop : )
10. I've always considered myself quite a solitary type and have always been comfortable with it but I've come to value the online community that I've come into contact with. All the wonderful, helpful and encouraging comments I've received in the past and the knowledge that there are a lot of people out there who care a little about me and my practice. It's probably more motivating than I realise.
11. The Cybershala, other blogs, other practitioners, some who I now consider friends whose own practice have an impact on my own. How our practices sometimes interact.
12. The feeling that whenever you get on the mat there is someone else somewhere in the world doing exactly the same thing. If they managed to motivate themselves to get on the mat then so can I.
13. Books, DVD's, YouTube videos. Educational, but also motivating, always a good idea if you feel your practice dragging a little. Pulling out one of the old DVD's to practice with has often helped.
God this is getting long, I'm on a roll.
14. The above is perhaps what motivates me to practice Ashtanga but what about what motivates me to get on the mat early in the morning for a couple of hours six days a week.
15. Routine is probably key. The practice is habit forming, you develop a craving and know that if you don't practice that day you'll regret it later. Feeding that routine is a good idea. Practicing in the same place at the same time. Same clothes, same mat, towel, same headband even. The mat in the same place, facing in the same direction. All these things help, I know because if I change anything it all falls apart and I become irritable, the practice doesn't work.
16. My half Waitrose pink grapefruit with honey on top. I only eat it if I practice.
17. Focusing on different elements of the practice. It used to be the Jump back, then it was the asanas themselves. later it was a meditative flowing experience and later still a kind of insight meditation going on throughout the practice. At the moment it's the breath and the bandhas. My whole practice is built on them, I adapt it to them, exploring this I find to be motivating.
18. A couple of months ago I became more interested in the tradition, and looking into that and trying to understand it a little more has also been motivating. By this I mean the changing nature of the practice over the last 80 years or so. But this also led to looking into the ancient tradition, the Yoga Sutras, the Gita, Upanishads etc. I think they all feed back into the practice and add to the general motivation. Chanting the Sutras has become a regular part of my practice now.
19. As we go into colder, darker mornings over here, making a feature of it by lighting a couple of candles has helped. I find I like practicing in candlelight. Bit embarrassed about it but I like it and it help get me on the mat so motivating.
20. Last, for now, but by no means least, the support and encouragement of my significant other has been and continues to be very motivating, thank you : )
But sometimes motivation is not enough and then it just comes down to discipline. Whether you feel like it at the time you just have to step on the mat and begin your practice. Conveniently your self-discipline improves along with the practice.
I find that not thinking too far ahead helps. On mornings when I lack motivation I try not to think past the first couple of breaths and then the first Sury Namaskara. The Sury's are usually enough, if not I just carry on through standing focusing even more strongly on the breath., still without thinking too far ahead.
I'll probably come up with others and add them when I think of them. Please feel free to add your own or which of these you too find helpful and motivating. I've probably forgotten the most obvious and important ones.