The easiest way will be to contact a law firm which deals with such issues. Firm will do everything for you, you will only need to pay the license fee - 1300 roubles, and its service. The procedure for obtaining a trading license is not fast: up to 30 days.
You must first decide in what form you will conduct trading activities. You can become an individual entrepreneur or to create a legal entity (e.g. LLC). Each of these forms has its pros and cons, influencing the trading activities. Individual entrepreneur does not comply with "the Order of conducting cash operations" and, therefore, entitled to dispose of the proceeds at its sole discretion, and OOO is obliged to Deposit the proceeds in the Bank because it funds a legal entity. In turn, individual entrepreneurs shall not be entitled to, for example, trade in alcohol, also, are imposed on them and other restrictions.
To obtain permission to trade the following documents are required:

1. the constituent documents of the legal person, the certificate of incorporation or certificate of registration of self-employment for the individual entrepreneur;

2. a certificate of registration in FNS;

3. for legal entity - full name and Bank details of the Director and chief accountant;

4. the lease of the premises in which you are going to trade;

5. conclusion of SES, GPN;

6. certificate from tax inspection about absence of debts in the city budget;

7. a contract with the organization, which is engaged in garbage removal;

8. the list of products which you will trade;

9. sanitary passport facilities for trade.
For trade in alcohol, also, need a license.

These documents are submitted to the Department of consumer market of administration of city district in which you are going to trade.
As a rule, permission to trade is granted for a period matching the term of the lease premises. However, if you are engaged in seasonal trading (e.g. Christmas market), that provides for a different period.