There's a lot to be said about good passwords. Here at ILJ Mail we try to enforce strong passwords by making sure they are at least 8 characters long and include an upper case letter, lower case letter, a number, and a special character. Those may not be easy for YOU to remember, though. I, personally, use a password manager and that helps a lot. There are many password managers out there to choose from. Some of the top recommendations from experts are LastPass, Dashlane, and others. (links from here do not imply that we back those products, we are just giving you a starting point to look at them). I suggest looking into it if you care about your security.
Here's a good article on passwords from Webroot (an antivirus company). Click here to read their article.
There's also a great comic by XKCD that tells another way of coming up with a good password:
I personally go with a combination of methods. My passwords are always more than 12 characters long and have upper, lower, numbers and special characters but I can remember what they are when I need to type them in just by reading them once. Along with a password manager, I feel as safe as I can be I suppose. You need to come up with your own methods that you can use but please stay away from simple one word passwords or just substituting numbers for the letters. If you do that, you might be sorry later that you didn't pay better attention to your security.