I never use to see specification earlier when purchasing mobiles but with time I realises having different parameters while purchasing mobile phones is really important.
One should first decide the budget in which he/she wants to buy a Mobile.
After budget comes the Brand or Company whose Mobile you want to purchase.
While looking at mobiles first of all have look at common things like style and design , camera quality, RAM, Expendable memory and and android type.
For smartphone you must check its processing and the features it have.
The quality of picture and sound is really must value in the Mobile one is buying.
The services or warrenty it is providing is really important aspects.
Hope these things really helped in deciding the mobile one wants to have.
Please do comment and ask any other things you want to ask.