Bookmakers accrue a vast amount of money from the Grand National and lots of it comes from punters who just blindly stick in a pin without giving it any thought whatsoever.
The Grand National is rarely won nowadays by a rank outsider and probably won't ever be so again unless the going is "heavy", i.e. lots of rain has fallen. Last year's winner, Mon Mome, which was 100-1, was an undoubted "blip" because his form suggested that he should never have been that price. He will be about a tenth of those odds for a repeat tomorrow, but with lots more weight on his back, he may well run another good race, but is very unlikely to win again.
A better class of horse has been competing in the race for many years now and that fact has been reflected in the horses which have won over, say, the past 20 years or so.
1. Do not bet a horse which has to carry more than 11st.
2. There is no value in the odds and approx 20 horses are liable to start at odds of less than 20-1 - disgraceful, especially when there is no guarantee that your horse will have the stamina for such an extreme distance unless it's competed and finished the race in the past.
3. Avoid betting any horse with an amateur jockey - the race is usually won by a horse ridden by a professional. Also, a female jockey has never won the race.
4. If your fancy is less than 9 years old, and more than 12 - forget it - pick something else.
5. The going is presently "good to soft", but if there was to be heavy rain before the big race tomorrow, it would change to "heavy", and unless you then choose a horse which not only has a light weight, but is proven on soft going, you will have no chance.
6. The only guarantee is that the bookies will win fortunes thanks to the mug punters.