When designing your application and an associated tool bar, consider the following issues.
Would the usability of the application be improved by placing these items on the tool bar?
Tool bars should only be used when they improve or enhance user access to common operations, such as in an application with several large menus.
What kinds of operations are being placed on a tool bar? How are they grouped?
Tool bars should present a natural organization of actions. Grouping items that are dissimilar can confuse users because they do not expect to find the item they are looking for in that context.
Is the tool bar too crowded?
Placing too many items in the tool bar can cause the user to have to search for the item they are looking for, rather then being able to quickly find it and use it. Keep the number of buttons to a minimum so that you don't increase the difficulty of your application when using a tool bar.
Are the icons clearly representative of their associated action?
Cryptic icons add to user confusion. Keep the pixmaps as simple as possible. Remember that all graphics must be international in scope. When designing a graphic to represent a command, such as Save, remember that the icon has to represent a verb, as opposed to a noun like most other icons. This can make the icon more confusing to users.