Hie Anita,
A humble advice to you would be to do a deep route study/ analysis of the various departments, branches, work targets and the employees of the company you want to carry out the PMS for.
You can prepare a Performance assessment questionnaire, which you can easily find on Citehr or anywhere on the web.
Select or edit the best set for you.
Get the form filled by the employee, his superior, HOD,the CEO or Chairman, and then put ur comments.
Then Select a method to analyse the filled formats.
If your PMS form awards ranks/numbers, base ur employees' increments on the basis of the points/ranks earned by them.
MAke out a table matching ranks with increment %ages.
E.g. could be, if Ram gets 8 marks he gets increment between 15-20% and if Sham gets 5 marks he gets 8-10% hike, or if Radha gets 3 marks she gets no increment for the year or may be even demotion(wch is a rare and a very strict case).
In the PMS you may also get to know if the employees are doing right, if they need any training etc etc.
Hope this helps..
Regards,
Parul