Dear Shalini
There can be two scenario related to fixation of Basic+DA.
1 Whether you want to comply at the minimum level. If so, than you have to check the notification issued by the appropriate govt. under the Minimum Wages Act, which further revised time to time as per the state norms.
2 If you want to keep the Basic+DA for an optimized CTC (Employee and Tax Friendly) than you have to consider many factors like:-
(Company budget, company strategy, No. of employee, employee category, future claims (EL, Gratuity, Bonus etc.), Salary revision policy etc.
Generally it should be 40%-50% of the CTC. A higher Basic+DA will attract more PF-ESI, Bonus, Gratuity Contributions and can decrease the “In Hand” salary. So in case of lower package employee, generally it is lower side (but should not be less than the MW Act).
You can consider the manually as well, but in such case you can face problem during salary revision, so it is advisable to link the basic with CTC.
Hope the above will clear you doubts. Fellow members can put more suggestions.