Engine Idle Problems

What is your question?

Whether the engine is hot or cold. when i just sit in there with the engine running, ill feel a slight shake and look at the tach and itll go from around 700-800 to 950-1000 for only a second. Other times itll go down in rpms, from the usual 750-800 down to around 600. This can get really annoying at times, Any suggetions or solutions of what i can do?