On the first you can start to dance with the partner you invited. On the second too, but less common. On the third or the fourth one, it's not a good idea to start dancing anymore. The tanda is practically finished and it is not respectfully towards your dance partner. You are allowing her only one or two songs. Sadly, this often happens when the leader doesn't know how the follower dances and wants to "test" her dance skills...
Also you could disturb the dance floor as the other dancers do not expect someone to start dancing at this time.
Before entering the dance floor, make eye contact with the leader that will be dancing behind and in front of you. Only after both of them having acknowledged the fact that you are about to go onto the dance floor, you can enter and start dancing.
Please notify your follower about this as well. We know that enthusiasm often makes you step onto the dance floor, not being aware of the people around you.
Respect the ronda
As a leader, do not initiate big or multiple back steps against the direction of the ronda. You cannot see what is behind you, you will most likely hurt somebody.
As a follower you can help your partner by holding him a bit tighter when there's a risk of bumping into the couple behind you.
The ronda usually consists of two outer lanes and the centre circle. The more experienced dancers dance on the outside, the less experienced on the inside. Respect these lanes, do not switch lanes unless there is a lot of space.
Do not overtake the couple in front of you. They will not be aware of you trying to overtake them and might engage a movement that ends on your or your followers toes...
Try to follow the couple in front of you. Try not to leave too big a gap. You will obstruct the fluidity of the ronda.
No bumper stickers
Please, leave enough space between you and the couple in front of you. If you dance too close, they will not have enough space to move. If they pause, you pause,... if they continue, you continue,...