Here are some sites for focusing on grammar:
The Azar Grammar website has PowerPoints that present the various grammar points covered in the Azar Grammar series:
Each of the Step Forward chapters include a grammar exercise. Here's a link to the Step Forward site. Make sure you click on your book image so you are on the right level.
A4ESL has lots of grammar exercises. They are divided into easy, medium, and difficult. The exercises are done by many different teachers in different ways so try more than one if you don't like the first one that you try.
Manythings.org has a grammar section. Some of the exercises link to A4ESL but some of them are just on many things.