Why do some places have rain frequently? There are some places on Earth which holds the record of being "The wettest place on Earth". On what factors these places differ from other normal places?

An example of wettest place on Earth is Cherrapunji

PS: Normal places doesn't include deserts.
The factors contributing to such differences between any given 2 locations are simply too numerous to be specific. From the top of my head : Hadley cell, local topography, source of humidity upstream (oceans, lakes, ...), etc...

In the case you are referring (i.e. Cherrapunji), this is mostly due to a combination of Himalaya (topography forcing), Indian Ocean (source of humidity), Walker circulation and the strong tropical evaporation at those latitudes (among other things).