Here are some sugestions to buy a mobile phone
Platform: there are 3 main platforms like Android, IOS, Windows. In this each has its speciality and features. For a normal user I prefer android.
Budget: decide a budget of yours to buy a phone and check the phones under your budget.
Check the specification and go for higher specification with in that budget. The specification should satisfy your needs.
Here are the minmum specification that should be choosed now a days.
Ram: 2gb
Storage : 16
Camera: 13 mp back and front 5 mp. ( check the pic quality)
Network: 4g with volte
Processor: octacore
Sound : check the sound clarity and loudness. With some high end phone also the sound will be too less.
Features: check whether the features of mobile is satisfying your needs like fingerprint, iris scanner, infrared, other sensors.
Screen size: go for 4.7 inch or above
Reviews : Before buying just check all genuine reviews about the phone. Like pros and cons.