A ‣ What are discourse markers? 
Discourse markers are expressions which organise, comment on or in some way frame what we are saying. An example is well.
A: So you live in Boston?
B: Well, near Boston.
Well here shows that the speaker is aware he/she is changing the direction of the conversation in some way (not giving the expected 'yes' answer). Another example is how teachers use words like Right and OK to organise what is happening in a classroom:
Right/OK, let's have a look at exercise 3.
B ‣ Organising a conversation 
Here are some common expressions which organise the different stages of a conversation.
Now, what shall we do next? So, would you like to come to the table now, please?
Good, I'll ring you on Thursday, then. Well then, what was it you want to talk about?
Now then, I want you to look at this picture. (said by someone in control of the conversation, e.g. a teacher)
Fine/Great, let's meet again next week, then, shall we? (often used to close conversations)
So, where was I? I was telling you about my aunt ... (often used after an interruption or to come back to the main topic or story)
C ‣ Modifying and commenting on what you say 
In these mini-dialogues, the expressions in bold modify or comment on what is being said.
A: It's cold, isn't it?
B: Yeah.
A: Mind you, it’s November, so it’s not surprising. (an afterthought, used like however)
A: What’s her number?
B: Let me see, I have it here somewhere … (a hesitation - gaining time)
A: It's quite a problem ...
B: Listen/Look, why don't you let me sort it out? (introducing a suggestion / an important point)
A: Would you? Thanks a lot.
A: And he said he was go-
B: Well, that's typical!
A: Hang on / Hold on! Let me tell you what he said! (preventing an interruption)
D ‣ Other useful discourse markers 
I can't do that. You see, I'm not the boss here. (explaining)
He was, you know, sort of ... just standing there. (hesitation)
He was wearing this, kind of / like, cowboy hat. (not sure of the best way to say something)
So that's what we have to do. Anyway, I'll ring you tomorrow. (the speaker thinks the topic can change or the conversation can now close)
It rained all day yesterday. Still / On the other hand, we can't complain, it was fine all last week. (contrasts two ideas or points)
We shouldn't be too hard on him. I mean, he's only a child. (making clear what you mean)
In informal spoken language, people often use the letters of the alphabet (usually no more than a, b and c), to list points they want to make.
STELLA: Why aren't you going this evening?
ADAM: Well, a) I haven't got any money, and b) it's too far anyway.
It is often difficult to hear these expressions when they are used in rapid speech, but when you are in a position to listen in a relaxed way to someone speaking English (for example, if you are not the person being spoken to, or you are listening to informal speech on radio or TV or in a film), it is easier to concentrate on listening for discourse markers.