Successful betting is not just about picking winners: it's also about whether it's worth backing them at the odds you are offered. The question to ask yourself every time is am I getting good enough odds to justify plonking down my money?

To find out, you have to use the same tools as we do - and you have to use your special advantage. That is that you are concentrating on just one race at one meeting on one day or on whatever single event you have picked on. We, on the other hand, have to cover hundreds of races and matches and events every day, and we can't get them all right.

The key questions I ask about every horse in a race - and you must, too - are as follows:

>> Has the horse won or been placed in a race of this class or above in the last 12 months?
>> Has it been placed on this or a very similar course recently?
>> Has it won over the distance?
>> Has it finished within half a length per furlong of the winner in either of its last two runs?
>> Has it registered an adjusted top speed rating (which you can find in the Racing Post) for today's race that is no lower than 75% of the highest rating for the race?
>> Has it been placed on today's going in the last 12 months?
>> Will it be inconvenienced by the draw?
>> Has it run within the last 50 days?
>> Has the jockey won or been placed on the horse before?
>> Has the trainer had three horses placed in the last fortnight?

As for other sports, as well as form, I try to take into account injuries and fitness, home advantage and weather. It's also worth bearing in mind facts such as that 28% of all football matches end in draws and British entrants are usually underpriced because too many punters bet on sentiment.

If you can get all these right, you'll know the true odds. The trick is to find races or events where I and my colleagues and competitors have got them wrong. If we have, you've found a value bet, and making value bets is the only way to beat the bookies.

When I first entered the business, the only sports covered, apart from horses and dogs, were one-offs - golf for the Open, tennis for Wimbledon and the odd major football match like the FA Cup final. Now there has been a mass proliferation, and people are betting on anything that moves - three tennis tournaments a week, for instance. It's been fuelled by the fact that there are now almost 100 online bookmakers and betting exchanges.

Our predictions are reflected in the early prices (also called tissue prices). We fax these over to the Racing Post every day at 4pm, so that they can be quoted in the next day's paper. We get hold of a copy of that at midnight, to see how our tissues compare with our competitors and make adjustments. As soon as we are open for business at 9.30am and we have started taking bets, the odds can often change dramatically in response to where the money is going.

For years, I just sat on my own with a pile of newspapers and cuttings, manually writing odds. Sometimes I got them right, sometimes very wrong. When I was working for Hills, I priced the golfer Ian Baker-Finch at 50/1 for the Open. The Post made him their headline tip and he won. The result was a loss of £250,000, and I was lucky to keep my job.

Arbsters and bookies can co-exist
We don't ban successful arbsters, but we know who they are and we watch their accounts very carefully, to make sure we don't catch a bad cold. You can't blame people for making free money. It's perfectly legal.

I have to admit that, if you are willing to put in the time and effort, invest in information technology, have a high degree of mathematical expertise, and are disciplined to regard arbitrage as a proper job, you can make a decent living by exploiting the differences in the prices offered by competing bookmakers. However, you sometimes have to spend hundreds of pounds to win less than a fiver.

The art is in finding the odds that are out of line with true probability. There are a lot of websites to help you, but you are better to do your own maths, because we are watching the percentages the comparison sites are publishing, too.

A good tip is always bet the 'wrong' price first, so that if we change the odds in response to a rush of bets, at least you are on the right side of the equation.

Click on the 'How To' button to view the odds chart, which is an essential tool. There are three columns. The first shows 84 possible odds, expressed as fractions. The third column is the same odds in decimals, the way the betting exchanges express them. The middle column is the vital figure - this expresses them in terms of a percentage. All the percentages in an event, added together, are called the overround when they add up to over 100 (and the overbroke when they add up to less - my nightmare).

What you have to do - and which we can do automatically, either with our software, or, after years of practice, in our heads - is to add up all the overround figures and make sure they come out at over 100. If, by combining all the best prices on all the betting outlets they are less, you've got us. And it does happen, more often than we like. Good luck in trying to find them!