By far the most important part of on page optimization, but you have to make sure that your meta follows certain specifics:

a. The title should not be longer than 77 characters in length.
b. The first three words of the title are your most important words and should be your attainable keywords, NOT your business.
c. Use pipes to divide your phrases so they look natural. An example for 'KidsStuff.com' would be:

Kids Furniture Online | Furniture For Kids Rooms | Only at Kids Stuff

If you had a localized store it could read:

Kids Furniture Online | Furniture For Kids Rooms | Only at Kids Stuff Los Angeles

77 Characters is a rule of thumb and what most professionals look at. A couple characters here or there isn't going to break the site but abusing the length will push the site to the bottom.

If your site has a built in CMS platform like Wordpress, Drupal, Magento, etc.. Most of them have a meta title counter so you don't have to count characters.

You also can have a developer build you a character counter if you have a custom CMS.