England have "a way to go" to find the consistency needed to top the Test rankings, says coach Trevor Bayliss.
A thumping 241-run victory in the first Test in South Africa was England's sixth win in 14 matches this year.
They regained the Ashes in the summer but lost to Pakistan in the UAE and drew with New Zealand and West Indies.
"There is still a lot of improvement in this team. It's only just the beginning of a journey for this young team," said Bayliss, who was appointed in May.
England, who are sixth in the Test rankings, needed only 24 overs on the final day in Durban to beat the team who top the standings.
|BBC cricket correspondent Jonathan Agnew|
|"Alastair Cook's tourists look as though they are enjoying their cricket and are playing it in a good spirit. I was very impressed with their performance.|
|"England have an excellent opportunity to win this series quite comfortably, so long as they do not succumb to their own inconsistencies."|
|Read Aggers' verdict on the first Test|
"If you want to be the best team in the world you've got to put in consistently good performances and I think we've got a way to go in that," Bayliss told BBC Sport.
"We can by no means rest on one win. We know it's going to be a tough series.
"We've only got to look back at the Ashes. We were up and down in results and that's one of the things we want to work on - consistency over a series."
Nick Compton, playing Test cricket for the first time since May 2013, made a watchful 85 in England's first innings, while James Taylor scored 70.
Joe Root hit 73 in the second innings to take his total for 2015 to 1,385 Test runs, while Jonny Bairstow added 79 from 76 balls to ram home England's advantage.
Moeen Ali was named man of the match after taking 7-116, but all of England's frontline bowlers took wickets.
Bayliss said: "I thought it was a team effort. Most guys scored some runs and the wickets were shared around as well."
The Australian added he was "a little disappointed" with England's scores of 303 and 326.
|Top six in world Test rankings|
|1: South Africa (114 points)|
|2: India (110 points)|
|3: Australia (109 points)|
|4: Pakistan (106 points)|
|5: New Zealand (99 points)|
|6: England (99 points)|
He said: "I thought we left 100 runs or so out there in both innings so we've got things to work on. Our bowling before tea on the fourth day was a little ordinary as well, but we regrouped and hit those right areas.
"The very best teams that get to the number one position in the world have one or two guys that will make 130.
"We had some guys bat very well for 70s and an 80 but if one goes on and gets 130, 140, 150, it could mean 100 extra runs and then the result is completely out of reach. That's something we will work towards.
"Most of the guys in this team are fairly young and inexperienced, so I think naturally that will come, but we've got to keep challenging them to do that."