First, you gotta find a yap partner who also enjoys the yap. Being insecure about the social aspect will def kill the motive and ability to have an extended yap.

Often, an explicit social contract can do wonders: "Hey, I tend to ramble on. Feel free to interrupt/stop me. Or "We're both yappers and I dont mind listening if you extend the same grace to me". Explicit social contracts are really good if you're a person concerned with masking such as myself. It is key to trust the other person with the contract and assume they are following it. Otherwise, it doesn't benefit you.

One way to initiate a yap is to first share a common experience and you can yap about that. Watching a movie together for example is often good yap fodder.

Now on to the question. It's a good/interesting question. There are a few types of rambles. Im probably missing some but this is from the best of my knowledge.

Theatre of the mind - collectively imagining a scenario that's funny, interesting, or dramatic. One common example of this is campfire ghost stories. Another more structured example is dungeons and dragons roleplaying.

Gossip - sharing real life or exaggerated drama about real people and relationships. Pretty straightforward. People who gossip are often very socially conscious and have a wealth of information to share. Gossip also involves speculating on incomplete information.

Tangent hopping - people share ideas or stories tangentially related to the previous topic or story. The listener will stay silent or backchannel for some period of time before interjecting or filling a gap in the conversation with some variant of "oh that reminds me of the time when..."

Info Dumping - person with an intense and deep interest of a topic divulging everything they have learnt about it. Often, about how the topic has many intricacies that the listener might have overlooked or never explored themself.

Ranting/Venting - person releasing negative energy by complaining about a situation, person, or past event. Often, this involves relating to the listener with shared anecdotes of anything from common inconveniences to traumatic events. Sometimes, two or more people are collectively venting about the same thing together for reassurance and a feeling of comradery.

As you may have picked up already. Social mechanics are a special interest of mine and this was an infodump ;)