Saints are unbeaten in their last four Barclays Premier League games and t he 29-year-old striker has scored 10 goals in the league this season
Long managed just five goals in the Premier League last season, his first at the club, and his manager is delighted with the improvement.
Koeman said: "I remember when Shane came, I think in all aspects he has learnt a lot.
"We did a lot with Shane in a lot of aspects of football and I think he is more complete as a player, as a striker.
"His pace, his timing, his movements are full of confidence
It is a big example that you can still learn when you are 26, 27, 28
You can learn every day.
"It is a big example of how you can develop with the help of coaches and that is nice to see.
"He was always really excited to come to Southampton and I remember talking to Shane about training sessions, ours are a little bit different to the usual English striker.
"He is really complete as a striker, in the box he is clever, he has a really good header, he makes it so difficult for the defenders because he is always on the move."
Former defender Koeman added: "I am happy I played before Shane was a striker."
Tottenham are the only top-flight team Koeman has failed to beat since he joined Southampton as manager in June 2014.
In his first season in charge of the club, he led Saints to a seventh-place finish with 60 points.
A win and a draw from their final two games - at Tottenham on Sunday and at home against Crystal Palace on the last day of the season - will see Southampton beat their best points total in the division, something Koeman would love to achieve.
He said: "I think that is the big example of what we are doing with Southampton in two seasons.
"We have beaten everybody once, only Tottenham we have not
It would be great to have a win this Sunday.
"Last season was great and if we do better than last season then that will be fantastic.
"We need at least one point (at White Hart Lane)."
Koeman remains determined his side have a chance of playing European football next season.
And if Liverpool beat Sevilla in the Europa League final and Manchester United beat Palace in the FA Cup final, eight English teams will be competing in Europe next season.
But Koeman is not leaving it to chance.
He said: "(Eight teams in Europe) would be great news for us and great news for English football.
"I was very happy about the final result of Liverpool
It is great for Liverpool and good to have an English team in the final
"First of all, if you can do it by yourself that is the best but if we need any help then we would like to have it.
"The team is full of confidence
We don't have injuries and the team is working hard, keeping the belief and keeping fighting for Europe
We are still in charge of that."
Source : PA