Good conversations have to built, sentence by sentence, give and take between two. One cannot start at the "end" the "good stuff" about one's own interests, one has to build a path to that place. With most people though, one has to build a path to a joint place that is not their subject or our own but a mutual one.

If there is no time to talk, you have to do the "Hi, how are you?/Bye" sort of conversations or, "What about this weather?" ones. So first you have to see who you are going to talk to and how much time you have to talk.

Talking to the grocery clerk when you are checking out is different than talking to someone in the bookstore who is looking at books in the same section you are and who looks friendly/nice and you'd like to try to talk a little about your subject with and that person is different from a classmate after class or during break who is different from a friend or relative you know pretty well.

First define the person.

The grocery clerk has limited connection with you. They are working and you are not for starters. It only takes 1-5 minutes to go through the line. So, you start with something referring to their job but not too personal. "I'm so sorry it is you in here working on this beautiful day and not me." That sympathizes with them having to work when you are not and talks about the weather (if it is raining you say something like, "I bet you don't mind being inside working on days like this!").

Some grocery clerks will just agree and not pick up the conversation. With them you know there's no where to go talking with them and so you say something lame like, "Yeah" and then stand there until they finish bagging your groceries and you're on your way. But others will add a bit of their information to your opening, "It doesn't matter, I get off in 15 minutes so have to go out in the rain anyway!" With them, you get to decide, do I continue or just say, "Oh, too bad!" and my groceries are bagged and I leave. If you have a large order, you can ask something a little more personal, since they "started" it. "Don't tell me; your car is in the last row of the parking lot and you don't have an umbrella?" The conversation isn't really going very far but you are both having fun and celebrating one's own life and the other's difficulties or rejoicing with them when they say, "No! My boyfriend is picking me up and waits for me right at the door!" You can then get even more personal and ask, "You all going somewhere to have some fun or just home where it's nice and dry?" You get to be a "voyeur" in someone else's life, get to learn a little about this other person and how they live and whether it is how you would imagine you would choose to live if you were them, etc. If they answer, "No, just going home," if there's still time, you can sneak in a bit about yourself if you want, "I'm going to a rock collecting convention and hope to pick up some Swan Peak Quartzite from Utah!" They may just look at you funny may ask you what part of Utah and tell you they have a friend who lives in Utah, or, may ask you the question you are hoping for, "What's so special about Swan Peak Quartzite?" and you are off for two sentences Or, they may just say, "That's nice." which is shorthand for, "I have no clue what you are talking about but am happy for you that you sound so excited about it." The key is looking for the "follow on" comment or question that lets you know it is your "turn" to add something. If you get a dead end comment like "that's nice" then it usually means that person is through and you might want to start on a different subject or a different person :-)