Are you willing to kill two birds with one stone? Here's a good chance. Not only can you learn and practice English but also you can donate rice to the hungry people around the world! Surprised, huh? But that's true! In www.freerice.com you can answer English grammar/vocabulary questions and for each answer you get right you donate 10 grains of rice through the World Food Program to help end hunger. Whenever you get a question wrong, Freerice will repeat it a few turns later to give you a second chance at it. The rice is paid for by the sponsors whose names you see on the bottom of your screen when you enter a correct answer. These sponsors support both learning (free education for everyone) and reducing hunger (free rice for the hungry).
The first questions may seem too easy but don't be mistaken. Freerice automatically adjusts to your level. It starts by giving you questions of increasing difficulty and then, based on how you do, assigns you an approximate starting level. 
There's much more to the website! So go for it and give it a try! Hope you like it!