Longer passwords are more secure

At a minimum, passwords should be longer than 6 characters, but a six character password most likely a weak password. Strong passwords are often 14 characters or longer. The easiest way to do this is to use more than one word.

Don't use single dictionary words

Hackers can easily break a password if it appears in any dictionary. This type of attack is so common it's called a "dictionary attack". To defeat this, use a made up "word" or multiple words.

Use symbols, numbers, ...

Use a mixture of uppercase and lowercase letters as well as numbers and symbols. "Dictionary attacks" also include adding numbers to the end of words, so something like "frequency123" is no more secure than "frequency". A more secure version might be "fr3qu3ncy!". (This is still not a very good password.)

Choose something memorable, such as a phrase or joke that you like.

Use phonetic spellings of words.