Second, Keybr.com measures your keystroke dynamics and collects comprehensive typing statistics. For example, it measures your typing speed for each individual key, and uses this data to generate random words putting emphasis on the weakest key. The more troubles you have with a particular key, the more you will be typing it. It means, the generating algorithm will put that letter in every word in the next generated lesson. Your typing skills are re-evaluated after every completed lesson, and the next lesson will be adjusted accordingly.
Also, something that I've found is that if you go wrong somewhere instead of mindlessly searching for the error (assuming there are multiple or you don't know the error's location) just start from the beginning and go down seeing that if this works. If you see a break and something disconnects, in all probability that's where the error is. It's all logic.