Farrell looks set to win his 50th cap against Italy at Twickenham on Sunday but says he does not even take a place in the team for granted.
The Saracens man has emerged as the heartbeat of Eddie Jones' side and may be moved from centre to fly-half for the visit of the Italians.
But Farrell thinks any complacency could lead to a fall in the standards which have helped England compile an amazing 16 victories in a row.
"I don't think you ever feel comfortable and I don't think that anyone here would tell you that they feel comfortable," said Farrell.
"And that's the way it should be, because there has to be a drive to constantly improve.
"I've not thought about winning the 50th cap too much. I need to get picked first and have a good week.
"The thing here is that it's all about getting better and I go on about it, but that's all I concentrate on."
Farrell made his debut against Scotland four years ago and agrees that he has developed into a more complete package as a player since then.
"I hope I have improved a lot and have come a long way since my debut," he said.
"It was alright - there were quite a few new caps at the same time as me, so there were a few of us in the same position.
"Of course I was nervous, you probably build it up into something that it is not. It is another game, but you are going into the unknown."
Farrell's development as a playmaker has accelerated under the guidance of Jones and the 25-year-old added: "The more aware you are of things, the more control you can have
"It's not something you can really work too hard on. I guess you can have an awareness of it and therefore be more in control of it."
