Using strong passwords for online accounts is paramount to their security. Short, easy-to-remember passwords can be easily cracked using simple techniques, and may compromise the security of your website or client data.
A strong password will consist of both upper-case and lower-case letters, numbers and symbols. It used to be safe to have 6 or 8 character passwords. But the increasing availability of high-performance computers has meant that these short passwords can be cracked within a few seconds! These days, passwords should be at least 15 characters long to be considered secure. If the website or service allows long passwords, you could consider using pass-phrases instead of pass-words. Online password generators are available can give you completely random passwords of any level of complexity.
If you are very concerned, you could use this tool by Microsoft to evaluate the strength of your password.
Another thing to remember is that you should never use the same password for accounts with more than one provider. If you use the same password for your online banking account and for some random website you signed-up to, you are basically giving the creators of that site access to all your money. Never use the same password for your email, your computer, your banking accounts or your work accounts. It compromises the security of all accounts which share the same password. If you find it hard to remember a long list of strong passwords (most people do!), you could consider using a password manager.