Here's my personal guide:
Outside of the above restrictions, pick anything you like. I use my full telephone number split into two digit numbers plus my birthdate (even if someone else uses this scheme, the chance of them having the same 6 numbers as me is extremely remote). Fortunately, all of these were under 50 and my phone number even reads perfectly left to right on my lottery ticket if I drop the birthdate ! Also, 3 of the numbers are above 31 and 3 aren't and there are no consecutive numbers. There is a 3-number multiple sequence (with an offset) though, but it's not a sequence someone would normally pick, so I'm happy with it.
IMPORTANT: Once you've selected your 6 numbers, stick with them ! People claim that they want to change their numbers each draw to either select numbers that have come up the most or the least. This is flawed logic I'm afraid, because the lottery does not depend on past history (unlike blackjack), so every one of the 14 million-odd combinations of 6 numbers is equally likely in every single draw. It's also the reason why writing a computer program to predict lottery numbers is a stupid and pointless task (just call the random number generator 6 times - that's just as good as any other method).
If you really must play around with a totally new set of numbers each draw, keep your original set of 6 going as usual and buy a second ticket. OK, so you are "throwing away" £2 a draw instead of £1, but at least you won't kick yourself if your previously tried and trusted "lucky numbers" win the very draw you decide not to use them any more. I'd recommend buying a second (or more) ticket when the jackpot accumulates because there was no winner the previous draw or because of an occasional "Super Draw" (where reserve money from previous lotteries is used to top up the jackpot prize).
Update:: Now that the main Lotto has recently changed to using 59 balls, my temporary advice is to include at least one of the numbers 50-59 in your ticket. I say "temporary", because eventually more and more people will start including 50-59 in their ticket (e.g. from first-time players). I wouldn't say this is a long-term rule and therefore it isn't included in my RKL random numbers algorithm. Don't forget that at around 10% of tickets will now be free Lucky Dips via a 2-match "prize" from the previous draw, so add that onto people who always play Lucky Dips (a lot I suspect), then you'll see that 50-59 will get some decent coverage right away anyway.