Cases selected u/s 147/148

First there should be concrete reason to believe that there is escapement of income .If the assessment for that year is already done under sec 143 then AO may have this concrete evidence or he could get this from other sources .
procedure to be followed by AO.
Get the approval from higher authorities for initiating 148 assessment,then issues notice to file the return for that year and with this 148 proceedings are initiated,and then same procedure which is followed for regular assessments under 143 is followed by issuing scrutiny notice ..

As per law, a valid notice must always be served before an assessment or reassessment. In case of reassessment the AO must record the reasons for doing so.