My hair has always grown fairly quickly, but I think it really began to grow faster once I began to wash my hair less. As I said, I wash mine one a week, although recently I've been able to push it to 8 days. Washing your hair, while getting rid of the dirt and products you've used, also strips the hair of its natural oils. So, leaving it as long as you can means those natural oils get to work on your scalp, and the length and quality of your hair benefits from it!
After shampooing twice and conditioning I let my hair air dry, only using a hairdryer if I need to be out the house quickly. If I do use heat on my hair, I make sure to use a heat protectant. I also avoid brushing my hair when wet, because it breaks the hair so easily. Between washes, I use dry shampoo to refresh my hair, and to create texture and volume. I tend to really need dry shampoo around the 4th day between washes, and it simply keeps the grease at bay until I choose to wash it properly. I also wear my hair tied up (usually in a bun) when I'm staying in the house, as I find this prolongs washing time. Plus, it just gets it out of the way!
So, yes, that's my very simple tip! Not only does limiting your washes promote growth in your hair, it just makes it healthier overall. I have found I have less breakages and my hair looks shinier and thicker since making this change about nine/ten months ago. I'm actually chopping about six inches off my hair the day this post goes up, so I thought I should make it now!