1. find a good stringing company, HK side will be in Causeway Bay, Kowloon side will be in Mongkok, San Po Kong one also good.
2. Do you like the string & the tension that you are using now? If yes, you can continue to use it, if not, you can ask their recommendation.
3. How long you play for month? If you play 1-2 hours per week, you can change the string around 3-3.5 months, but if you play more, you need to change it shortly.
4. Price - depends on which string you choose, from $130 to $400