Hard and soft limits
A hard limit is something a person will not do, full stop. A soft limit is something they might be open to in the right circumstances, but only after it has been discussed, never assumed. Both are said out loud, in advance, by both people.
Safewords
A safeword is agreed before anything starts and means stop, immediately, no questions asked and no need to justify it. Choosing a word that would not come up naturally in conversation makes it clear when it is used.
Checking in
Checking in during and after is normal and expected, not a sign that something has gone wrong. It is simply how two people confirm things are still working as agreed.
Stopping without an argument
Either person can stop at any point, and that decision does not need to be negotiated or justified in the moment. A safeword or a plain "stop" means stop. Working out what happened, if anything needs discussing, comes afterwards, not during.
Why this is not a manual
This page describes how people agree things, not instructions for specific physical practices. What any two people actually do is between them, discussed in the detail they need, not laid out generically here.
How this connects to safety
This is also a safety subject, not just a technique. Safety on Date a Domme covers the wider picture, including what to do if someone will not respect a limit or a safeword.