Generally you should avoid using the default database role (often postgres) in your application. You should instead create a user with lower levels of privileges. Here we make one called niceusername and give it a password very-strong-password

CREATE ROLE niceusername with PASSWORD 'very-strong-password' LOGIN;

The problem with that is that queries typed into the psql console get saved in a history file .psql_history in the user's home directory and may as well be logged to the PostgreSQL database server log, thus exposing the password.

To avoid this, use the \password command to set the user password. If the user issuing the command is a superuser, the current password will not be asked. (Must be superuser to alter passwords of superusers)

CREATE ROLE niceusername with LOGIN;
\password niceusername

To support a given application, you often create a new role and database to match.

The shell commands to run would be these:

$ createuser -P blogger
Enter password for the new role: ********
Enter it again: ********

$ createdb -O blogger blogger

This assumes that pg_hba.conf has been properly configured, which probably looks like this:

# TYPE  DATABASE        USER            ADDRESS                 METHOD
host    sameuser        all             localhost               md5
local   sameuser        all                                     md5

Suppose, that we have three users :

1. The Administrator of the database > admin
2. The application with a full access for her data > read_write
3. The read only access > read_only

--ACCESS DB
REVOKE CONNECT ON DATABASE nova FROM PUBLIC;
GRANT  CONNECT ON DATABASE nova  TO user;

With the above queries, untrusted users can no longer connect to the database.

--ACCESS SCHEMA
REVOKE ALL     ON SCHEMA public FROM PUBLIC;
GRANT  USAGE   ON SCHEMA public  TO user;

The next set of queries revoke all privileges from unauthenticated users and provide limited set of privileges for the read_write user.

--ACCESS TABLES
REVOKE ALL ON ALL TABLES IN SCHEMA public FROM PUBLIC ;
GRANT SELECT                         ON ALL TABLES IN SCHEMA public TO read_only ;
GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public TO read_write ;
GRANT ALL                            ON ALL TABLES IN SCHEMA public TO admin ;

--ACCESS SEQUENCES
REVOKE ALL   ON ALL SEQUENCES IN SCHEMA public FROM PUBLIC;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO read_only; -- allows the use of CURRVAL
GRANT UPDATE ON ALL SEQUENCES IN SCHEMA public TO read_write; -- allows the use of NEXTVAL and SETVAL
GRANT USAGE  ON ALL SEQUENCES IN SCHEMA public TO read_write; -- allows the use of CURRVAL and NEXTVAL
GRANT ALL    ON ALL SEQUENCES IN SCHEMA public TO admin;

With the below commands, user's default search_path can be set.

1. Check search path before set default schema.

postgres=# \c postgres user1
You are now connected to database "postgres" as user "user1".
postgres=> show search_path;
  search_path   
----------------
 "$user",public
(1 row)

2. Set search_path with alter user command to append a new schema my_schema

postgres=> \c postgres postgres
You are now connected to database "postgres" as user "postgres".
postgres=# alter user user1 set search_path='my_schema, "$user", public';
ALTER ROLE

3. Check result after execution.

postgres=# \c postgres user1
Password for user user1: 
You are now connected to database "postgres" as user "user1".
postgres=> show search_path;
 search_path 
-------------
 my_schema, "$user", public
(1 row)

Alternative:

postgres=# set role user1;
postgres=# show search_path;
 search_path 
-------------
 my_schema, "$user", public
(1 row)

Suppose, that we have three users :

1. The Administrator of the database > admin
2. The application with a full access for her data > read_write
3. The read only access > read_only

With below queries, you can set access privileges on objects created in the future in specified schema.

ALTER DEFAULT PRIVILEGES IN SCHEMA myschema GRANT SELECT                      ON TABLES TO read_only;
ALTER DEFAULT PRIVILEGES IN SCHEMA myschema GRANT SELECT,INSERT,DELETE,UPDATE ON TABLES TO read_write;
ALTER DEFAULT PRIVILEGES IN SCHEMA myschema GRANT ALL                         ON TABLES TO admin;

Or, you can set access privileges on objects created in the future by specified user.

ALTER DEFAULT PRIVILEGES FOR ROLE admin GRANT SELECT  ON TABLES TO read_only;

CREATE USER readonly WITH ENCRYPTED PASSWORD 'yourpassword';
GRANT CONNECT ON DATABASE <database_name> to readonly;

GRANT USAGE ON SCHEMA public to readonly;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA public TO readonly;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO readonly;