Hi there,
I think at 6 months, DS will learn how to soothe himself to sleep most quickly from pick up put down. At six months you do this by using your voice to reassure DS and when he gets upset that you are not patting him, pick him up, gently lay him into a horizontal position and reassure him 'its bedtime honey...' and gently lay him down. Try not to make eye contact whilst reassuring him, he can't help engaging with you if you do.
You may also have to help him to control his arms and legs, as at six months once he starts to flail, he does not yet have the skills to calm himself. Most six months are no longer swaddled, so you could just wrap a blanket around his arms and legs.
Good luck and let us know how you get on - the big big key to PU/PD being successful is consistency, so once you start, keep going until he is asleep - I always found it handy to dig out my baby whisperer book before attempting something new with Mads and read up on it, also having it to hand for reassurance whilst doing something new, helped me to stick with it and not cave in.
Take care
Dee
x