Gambling astrology is a methodology to help you determine the best time to take a risk. This doesn't necessarily mean you'll be a winner every time, but you could increase your odds somewhat.
Planetary transits and alignments are key in gambling astrology. This area is ruled by the Fifth House, which is the House of Speculation. Those who look to take risks want to be influenced by this House. Another strong influence are the Fire Signs (Aries, Leo and Sagittarius), as they are quite risk-friendly. If you have the fire element strongly in your chart, you could hold a winning hand. Conversely, the Earth Signs (Taurus, Virgo and Capricorn) are the most risk-averse as they speak to hard work and keeping one's money. Take no chances if these signs are hanging around!
If Jupiter, the Planet of Expansion, Luck and Good Fortune, is transiting your Fifth House, it's definitely the time to take a risk. Depending on their alignment, other Planets can exert influences which should be monitored if you are thinking of taking a risk. Mars is the Planet of easy come, easy go, so be prepared if it's in your chart. Saturn won't yield great rewards, but it will allow you to stay in the game for awhile. Where Uranus is concerned, what you should expect is the unexpected. Neptune is associated with wild speculation, while plucky Pluto symbolizes the biggest crapshoot of them all!
With odds like this, gambling may not pay off in the end. It's your bet to make.