Defoe came off the bench on Friday to earn his 55th cap, although the night proved to be an unhappy one as England lost 2-0 to Chile.
Defoe has been getting used to life among the substitutes recently. This time last year he was a regular for club and country, but he has started just once for Spurs in the Barclays Premier League this season and had been an unused substitute in the previous six England games before the Chile encounter.
The 31-year-old is averaging 16.7 minutes per league game this season and he knows that must change if he is to make Roy Hodgson's 23-man squad for Brazil.
"Getting into a World Cup squad is based on merit and you have to play for your club," said the Tottenham striker, whose only league start came against West Ham last month.
"As a forward, if you are not getting the opportunities to play it will be difficult.
"Frank Lampard got it right when he said the other day that everyone is fighting (for places).
"It's important that everyone goes back to their clubs and plays games to try to impress the manager.
"It's a long way to go before the World Cup. There is a lot of football to be played and we will see what happens. You never know, I might play every game from now on."
Defoe has kept his place in the England squad thanks to his superb form in the cup competitions, scoring nine times, but Villas-Boas' refusal to drop Roberto Soldado means he may have to wait a while for another opportunity in the league.
The former West Ham man, who has 19 England goals, did his best to impress Roy Hodgson on Friday, combining relatively well with Wayne Rooney during his 24 minutes on the pitch.
The striker knows losing their 10-match unbeaten run is not good news for England heading into a World Cup, but he thinks Hodgson did the right thing by rotating his line-up.
"It's not good losing, especially at home," Defoe added.
"You want that winning mentality going into a World Cup but there were spells where we did well and created some good chances, it could have been a different game had we put them away.
"Chile are a clever side but I suppose there are positives we can take out of the game.
"We were playing against a side who are technically good, and kept the ball so well, but it was important for the manager to see other players and give them an opportunity to see what they can do at this level."