Tuilagi was cited for a tip tackle on scrum-half Danny Care two minutes into Leicester's Aviva Premiership final defeat to Harlequins on Saturday.
The Tigers centre was cleared at a disciplinary hearing last night after England lawyer Richard QC successfully proved that Care's knee had hit the ground before his torso.
Although Tuilagi was shown to have controlled Care's return to the ground on this occasion, Lancaster stressed the need for him to remain vigilant.
"I have had a one-to-one with every member of the touring party. I had a good conversation with Manu on the strengths of his game and the areas we need to make sure he is on top of," Lancaster said.
"Part of that is tackle technique and discipline. He understands that. He is a young player and still getting experience."
The independent disciplinary panel backed referee Wayne Barnes, who penalised Tuilagi for the tackle but ruled the tackle was "not dangerous".
It could have been worse for Tuilagi given the International Rugby Board's clamp down on dangerous tackles.
"I was relieved. There was a concern," Lancaster said.
"I am pleased to see the people in charge found it was dealt with on the pitch at the time. I am delighted he is available."
Lancaster has extended the warning to the whole of his squad ahead of their three-Test series against the Springboks.
"The directive is clear and players are working hard to abide to that," Lancaster said.
"It is a difficult one, an 11-stone scrum-half comes running at a 17-stone bloke. Danny said the force of the impact took him off his feet.
"People recognise Manu's intention was not to hurt anyone.
"We all understand the reason the rule is there. Players just need to be careful if you are picking somebody up.
"When we do video sessions we will highlight areas of 'red flag' - things such as the directives around the breakdown, competing for the ball when the referee calls ruck, being onside and tip tackles."
Once Tuilagi was cleared to play on, Lancaster's concerns then switched to the foot injury he suffered in the Premiership final.
Tuilagi was cleared to fly with the squad tonight but he has not trained since the game.
England will know on Friday whether he is fit for a return to action next week, ahead of the first Test in Durban.
Phil Dowson, Anthony Allen and Ugo Monye all sat out training today but are expected to be available when the team begin preparations on arrival in South Africa.
England have never before faced the Springboks in a three-Test tour and they have organised two midweek matches, with Lancaster taking a 42-man squad.
"It is a fantastic opportunity to pit ourselves against one of the best rugby-playing nations in the world," Lancaster said.
"It as a great opportunity for England. We spoke last night about being good ambassadors on and off the field. That is what we want to achieve going into the tour."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.