Modified Missionary – Normal guy on top sex doesn't do a whole lot for the G-Spot, but it can easily be switched up for more G-Spot contact. Have her put a pillow or two underneath her bottom, and put her legs straight up in the air. Slowly enter her, and put her feet flat on your chest. The pillow changes up the angle of penetration, aligning the penis with the G-Spot for every thrust.
Girl on Top – When a woman is on top, she has total control over the depth and angle of penetration. The easiest way to provide direct G-Spot stimulation is to have her lean back slightly, and keep her knees on the bed. This will angle the head of the penis directly into the G-Spot.
Doggie Style – This position is foolproof, simple, and successful. Have her bend over, and gently enter her from behind. This position allows for very deep penetration, with direct G-Spot stimulation. For an extra kick, encourage her to rub her clitoris. Just make sure you don't thrust too deeply, you don’t want to miss the spot. Focus on slow, shallow thrusts for the best results.
Spooning – Not only is this position very simple, it is great for stimulating the G-Spot. Both of you should lie on your sides, with you behind her. Hold her top leg up, and enter her from behind. Put your arms around her, and slowly rock your way to orgasm. The head of your penis will be in perfect alignment for direct G-Spot contact in this one, so expect her to orgasm early and often!
Reverse Cowgirl – Basically the same as girl on top with a little more difficulty. The man puts his knees together, and has her straddle his penis while facing away from you. Encourage your partner to gently rock back and forth. While in this position, the G-Spot is directly stimulated by the penis head and shaft. Be sure to use lots of lube to keep your penis inside her.