If you are planning to invest in a mutual fund, then the better way to do is through an SIP (systematic investment plan) instead of lumpsum.
An SIP can help you average out the cost of acquisition of mutual fund units, thus maximising your chances of earning higher returns.
There are some investors, meanwhile, who believe that investing in an SIP on a particular date makes a difference to wealth creation. For instance, does it matter whether the date of SIP is 7th or 15th?