Do not use do and a- together. Do things, something, anything (NOT do an a-).
ꭗ I have a number of actions to do today.
ü I have a number of things to do today.
ꭗ We should do a- to help him.
ü We should do something to help him.
Use an act or the act of (doing) something (NOT a-).
ꭗ She was caught in the a- of stealing during the night.
A- is uncountable when talking about the idea or process of doing something.
ꭗ We urge the authorities to take an a- soon.
ü We urge the authorities to take a- soon.