Dear Sir,
You have to take into consideration a few factors for retrenching the employees, first of all whether it is a mfg co or a services company. What is the strength of the company, if it is mfg and strength of workers exceeds 100, you need to seek Govt permission prior to retrenchment. If not, then you need to put up a seniority list of all the workers atleast for 8 days then you can resort to retrenchment on the principle of 'last come first go' ie the employee who joined last will go first and so on. Then, you need to compute the retrenchment compensation which is 15 days salary per completed year of service and one months notice pay at the time of retrenchment i.e. simultaneously. These are the provisions of the Industrial Disputes Act, 1947.
As regards poor performance of employees you have to take disciplinary action and if proved in the enquiry, then only you can terminate them after considering their past record and depending on gravity of misconducts.