Although sophisticated computer and internet monitoring devices can delve deeply into even the best-protected computers, if someone is really determined, a strong password is the best protection for your online activity. The trouble with staying safe online is the need to have multiple, unique passwords so that a "spy" can't easily follow you around from the dating site profile through to your online banking.
Keeping track of multiple passwords can be problematic. There's the temptation to record passwords on reminder notes (not safe at all!) or revert to using the same details everywhere (also not a good idea). If you are going to keep a note of all your passwords, do store them on an encrypted USB stick, within a password-protected document. Here are some tips on how to create memorable passwords which nosy people won't find so easy to crack.
Book references
This old spy trick is a good one. Choose a book from your bookcase, pick a number and, go to that page, then note the first (or last) word on that page. Keep using that book and that format for all other passwords you set up. To make it easy to remember, you could use a number that is meaningful to you - but all you need to remember is the number, in this case, as you have the book to refer to. For example, using that old children's favourite, "Watership Down", you can end up with Yelping411 and Weakened393 - not obvious password choices at all.
Simple ciphers
Most of us begin with a simple, meaningful word to base a password around; the name of a pet or a child, a nickname or a place we love. Unfortunately, these easy-to-remember words are also easy for people to guess, especially if you talk about the pet, child or location on social networks. All is not lost - by using a very straightforward code, you can still create an interesting and memorable password - just as long as you remember what your code is.
For example, if Fluffy was your beloved pet rabbit, you could use this by spelling out the password with the numerical placing of the letters in the alphabet - 612216625, perhaps adding the first and last letters F612216625Y for a strong mix of letters and numbers. For those of us with better memories for words than numbers, use a classic cipher which replaces letters. In this case, F could be the equivalent of A; thus; all other letters shift back five places. Fluffy would then read as AGPAAT. Again, mixing letters and numbers is recommended, so you could use 612216625AGPAAT for your fluffy-related password, and nobody would work that out.
Mnemonics
Clara in Doctor Who used the mnemonic "RYCBAR" for "run you clever boy and remember", even though (thanks to timey-wimey reasons) she didn't know why this mnemonic mattered to her so much. The trick is obviously to pick something meaningful that you wouldn't forget or get confused about. How about FWMFP, "Fluffy was my favourite pet"? Or IMMWI10, "I met my wife in '10"? You could also use a line of dialogue from a favourite film or lyrics from a song. Just as long as you don't scribble down passwords on a Post-it note...