(1) Set a limit. Players who set a limit on how much they are prepared to lose, or can afford to lose, avoid disasters, financial or emotional. This applies to the National Lottery as much as other bets. Playing the Lottery is particularly insidious, simply because the money spent on tickets looks like small change. However, it adds up.
(2) Set a limit on what you hope to win. This might seem a paradox, because in a sense you can let the upside rip. Still, it is a good idea for anyone going racing or stopping by a betting shop or visiting a casino to have an idea of what they hope to win. Suppose you start out winning (as does sometimes happen) and get well ahead. Why not hang on to it? - at least for that day.
Many punters get the idea when they are playing up winnings that they are on a free roll, gambling with their (the bookie's) money. Not so: they are playing with their own money. Better to entrust half your winnings to a friend and splurge the rest.
The most important New Year's resolution in gambling is to understand what you are doing. Reconnaissance, they say, is never wasted.
Whatever kind of bet you favour, from a light flutter on the Lottery to high stakes speculation on commodity futures, there is no substitute for understanding the market and the odds. The aim is to find VALUE - bets where the odds seem to be in the player's favour. This can happen quite frequently in sports betting, as in political bets, or in currency markets, when punters can exploit the difference between their own judgement in estimating the outcome and the odds quoted. Even when, as usually happens, the odds are unfavourable, it is prudent to evaluate the downside of the gamble. That is what Girolamo Cardano attempted, in studying the theory of probability 450 years ago.