The Perfect String
When somebody asks me to string a racket for them, I don't simply take their racket and put my choice of string/tension in it. Often I'll know the player, meaning that it's a bit easier to advise as I'll know how they hit the ball, their general style of play, how much cut/spin they use or whether or not they struggle with power, for example. This can aid me in helping them choose the best string type and tension.
It gets more tricky when I don't know the player... and especially if they give me a racket that's still got the original factory strings in it. So, I generally go through a check list:
1) Ask if they like how the current strings play - can be a starting point
2) Ask if they've tried specific types of string previously, and if they have a favourite.
3) Do they know what tension works best for them.
4) Check if they're a power/touch player or a mix of both.
Based on the above, I'll be able to get a fairly decent picture as to what strings to put in. Remembering that certain strings perform very differently when on different rackets, so it's good to offer advice based on experience. For example, I would probably shy away from putting a thin string (Tecnifibre 305 1.10 springs to mind) on a racket with a large head. Although you may get some decent initial performance, the durability will be questionable given the extra force going through the strings. Warnings are given as standard in this type of scenario!
No player is the same. I've strung rackets for pro's who've told me to stick what I'd consider basic, factory strings in their rackets and equally I have many club players who are very picky with their string choice and tension. Lessons I've learned are to listen to the customer, offer sensible advice and to use my experience as a player, coach and stringer when helping them to decide their next string choice.