Restrict SQL Server Login access to only one database

I think this is what we like to do very much.

--Step 1: (create a new user)
create LOGIN hello WITH PASSWORD='foo', CHECK_POLICY = OFF;


-- Step 2:(deny view to any database)
USE master;
GO
DENY VIEW ANY DATABASE TO hello; 


 -- step 3 (then authorized the user for that specific database , you have to use the  master by doing use master as below)
USE master;
GO
ALTER AUTHORIZATION ON DATABASE::yourDB TO hello;
GO

If you already created a user and assigned to that database before by doing

USE [yourDB] 
CREATE USER hello FOR LOGIN hello WITH DEFAULT_SCHEMA=[dbo] 
GO

then kindly delete it by doing below and follow the steps

   USE yourDB;
   GO
   DROP USER newlogin;
   GO

For more information please follow the links:

Hiding databases for a login on Microsoft Sql Server 2008R2 and above