Choosing a racquet string and tension.
Alright, this is just a little education on some of the strings and how to decide on tension.
There are so many strings out there and it is quite tough deciding on what to use. I hope this will help.
String gauge: 16 gauge, 17 gauge, and 18 gauge. The lower the number, the thicker the string. If you want more topspin, go with the thinner 17 or 18 gauge string. If you break strings a lot, go with the lower 16 gauge, or go with a more durable string like polyester or kevlar in a 17 or 18 gauge. The 17 and 18 gauge strings will open up the string bed, but will break quicker.
Durability: If you want true durability, use kevlar or polyester as your mains (the up and down strings) and a softer string in the cross strings. This has to be strung as a two piece string job. There are some more arm friendly strings out there that have a little durability, but nothing like the polyester or kevlar strings.
Arm friendly strings: Gut, Gamma Live Wire, Gamma TNT, Wilson NXT, and Wilson Sensation are all very soft and easy on the arm. However, they break quickly and you must pre-stretch them or double pull them when stringing so that they are stretched a bit before locking them in. They will lose tension and be like a trampoline if you don't do that. Great strings for people with arm problems.
Playability strings: Gut, Gamma Live Wire, and Wilson NXT are my choices for ultimate playable strings. I recommend stringing these strings in the upper recommended tension range of your racquet. Don't worry, they are soft and have tons of resilience. They really will put a bit of power into the ball. Especially gut.
Tension: Again, go with a higher tension for more control and a lower tension for more power. I always recommend going with the higher tension and using a lively string to give you the extra "pop" on the ball. Keep the racquet within the recommended stringing range or a couple of pounds above or below. The manufacturers have experimented with all of this and know where the racquet performs its best.
Hopefully this will help a little. I have tried everything out there in terms of strings. I've had numerous sponsorships with string manufacturers (Babolat mainly) and I've had the best and worst of luck with them all. I must say that I have been most impressed with Wilson strings. They really make a tremendously playable string. I used to go through 2-3 racquets every day until I began stringing with Kevlar and then polyester. Synthetic gut lasts me an average of 30 minutes to an hour. I therefore use an ultra playable string on my crosses and a polyester for my main strings. I pop strings about every other day now. No biggie. I hope this gives a little insight on the subject.:)