Here is a simple recipe
* Choose a long random password >10 or 12 chars
* Modify the password with something from the website, like add the first two characters on position 3 and 9.
First of all a long random password is secure (in the sense it is hard to crack). Adding something makes it no less secure. The adding is just for making it unique for each website.
Second, you can remember one long random password, trust me. I can't memorize many random passwords and not the right one's for each website, but I can memorize one, so can you. This is especially true, as you are using it many times a day (and don't let the browser remember it for you).
This does not work well on mobile, because long passwords on tiny keyboards are error prone. Nothing is perfect :-(