There are numerous synonyms for the phrase "do something for." For instance, you could use the term "assist" to imply that you are providing aid for someone else. Alternatively, you could use "help" to describe a situation where you are supporting someone in achieving their objectives. "Aid" is another term you could use when you're describing giving help to someone. "Satisfy" could also be used to portray the idea of doing something for someone when it is meeting their needs. "Serve" is another synonym that captures the concept of doing something for someone, especially when it is a paying customer. Ultimately, there are many ways to describe serving someone, providing assistance, or helping someone else.