Thanks for writing. Unfortunately in your area it's too cold to grow avocado outdoors --- so for you, it will have to be an indoor tree that you move outside for the summers.
Like most houseplants, water it enough that just the top inch or so of soil dries out and grow it in the brightest spot you have. If it starts to get too tall, feel free to prune it back to make the plant grow bushier. If you'd like it to grow faster, use a general-purpose fertilizer (following the directions on the fertilizer packaging) during the spring and summer months.
---Justin, Senior Garden Editor, BHG.com