Playing someone with a weak second serve is a huge advantage to the player returning serve.
A weak second serve is like a short ground stroke that you can hit offensively to take control of the point. Being aggressive and taking control of the point from the return of serve will increase your chances of winning and staying ahead in the match.
There are several advantages to attacking a weak second serve. "Attacking" the serve does not mean that you have to hit the ball hard or even hit a winner. You may wish to attack by hitting aggressive topspin to your opponent's weaker side, or slice a ball low to the side they have trouble hitting low balls with.
The point is that you have more time to prepare and to execute your shot, so take advantage! Hit to their weaker side, hit the ball in the corners or hit an approach shot and come to the net, then finish off the point. Your options really open up when you play someone with a weak second serve.
Mentally, there is a large advantage as well. When your opponent knows you are going to attack their second serve, it puts more pressure on them to get their first serve in.
It also may force them to try and hit too much on their second serve and force some double faults, especially on the big points. This makes it much harder for your opponent to hold serve and can help you to have more confidence when trying to break serve.
Here are some strategies for attacking weak second serves. There are a lot of options, being able to use all of them and mix them up will be to your advantage.
Chip and Charge
This is a dying art of tennis because there are not too many serve and volley players anymore. However, this does not mean that this form of attack cannot be effective. Chip and charge is when you take the serve on the rise and slice your return, close into the net and wait for the return. I like this tactic because it keeps the ball low and puts immediate pressure on your opponent.
Hit a hard approach shot off of the serve and come to the net. Even though this sounds similar to the chip and charge it is different. This allows your opponent less time to get to the ball and hit their next shot since you did not slice the shot. You can hit with tons of topspin to make it bounce high or just hit the ball flat, either way it puts immediate pressure on your opponent while putting you in a great position!