I've been spraining my ankles for 35 years, especially the left ankle, which I dislocated in my 20s jumping off a climbing wall and landing on the edge of the cushion. Now that you've done it that ankle will always be weak so take care to be mindful of where you place your feet; sprains always happen when you are not paying attention. My last sprain was last month, walking through a hotel car park in Sudan where they paint the edges of the kerbs with gloss paint and my foot slipped off the edge, spraining the ankle and sending me sprawling in the dust. A week later I was walking along in London and it went over again on flat pavement, much worse. It was swollen, blue and yellow and I actually thought I might have broken it but now, three weeks later, it has almost recovered.
As others have written: Rest - Ice - Compression - Elevation. Go and buy a tubular elastic bandage, double it and wrap your lower leg from below the knee to the toes in doubled bandage. After a week it will begin to irritate you so cut it in half and just use one thickness until a week later when you'll want to remove it. You can see an orthotics specialist who can help you to avoid sprains by making up a thin wedge to go under your insole, which will cant your foot bones slightly inwards. This will take a long time on the NHS, cost about £250 privately or £50 if you enquire at your local medical school because the orthotics department is always in need of chronic ankle sprainers (which you are now) on whom their students can practice. If you live in the NW, Salford Uni Medical School offers this service. It's not quick, I may need to wait now until the new academic year but I've been prone to sprains for 35 years so another 6 months doesn't matter.
Buy a circular wobble board and have a couple of sessions a day at home, they really do help.
Above all be mindful of where you place your feet when walking or this will happen again and again because you have now stretched and weakened the ligaments and tendons that hold your very complex ankle together.