I'd start doing some basic things like walking, stepper machine or cross trainer to get yourself back into it. While slowly increasing the intensity of exercise.

Also consider ankle strengthening exercises, like just standing on one foot for a while. Invest in an ankle brace, trust me once you do an ankle they stay weak for a long time. Make sure you have adequate footwear which gives the support you need and that you aren't rolling your leg outwards as you run. A wobble board is also very helpful for increasing ankle strength and balance, but be careful with this at the start so you don't blow out the ligaments.