This very much depends on what it is that you are trying to accomplish. There are hundreds of commands that can be used to maintain an AIX machine. If you are more of a GUI person, there is SMIT:
This will launch a curses interface that will allow you to do just about anything you want. Some things can only be done through SMIT, unless you have a penchant for 100+ character commands. Once you get familiar with certain tasks, you can append keywords, known as "fastpaths" to that command to jump right to the task:
Hardware maintainence and troubleshooting can be done with diag: