Unless of course the character is a robot  

But yes that is good advice for dialogue. If you have willing friends and family, asking them to run some lines is a good way too. Although my other half is sick of that now so I dare not ask her anymore.

Final Draft has a speech capability (will read the script to you). If you use FD, that's a good tool as well to catch the mundane

My FD man and woman voices sound robotic. I don't find them particularly helpful.

I agree though that bad dialogue when heard is a good way to learn what not to do.

I have a way of writing natural dialogue that IMO sounds close enough to real speech, without the transactional nature of fictional dialogue.

Basically if I know a scene needs an important back and forth between two or more characters, I will write the entire conversation for as long as or as short as needed with no immediate consideration for plot contrivance or narrative. If the scene is taking place at a meal, I will just start writing the beginning of the conversation and keep going until after everything necessary for the scene has been established organically - the character's state of mind, any story beats.

Then I go back and cut out everything leading up to that point that isn't necessary and everything afterwards, keeping the scene to the point and immediate, as if the viewer walked into the room partway through a conversation. Basically, by acknowledging that viewers will "fill in the blanks" on most missing context and not feeling the need to explain why a character is talking about something, you can be both efficient AND natural.
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And when you're comfortable staying on a scene for longer than narratively necessary (eg for atmospheric or tonal reasons), you keep in more of the conversational context.

(Writing this out made me realise how overengineered this seems, but I enjoy writing dialogue).

Quoted from AlsoBen I have a way of writing natural dialogue that IMO sounds close enough to real speech, without the transactional nature of fictional dialogue.

I have a way of believing all my dialog sounds perfectly natural.  Then I post my script, and read the reviews...

Script dialogue is interesting, and hard to judge your own work sometimes.

Just look at the current OWC reviews, you will see the same script get comments like 'dialogue sound natural' and 'dialogue sound stilted and unnatural'.

So I think the tips above are all valid and useful, but sometimes you need to trust your voice too... imho of course.

Quoted from LC My FD man and woman voices sound robotic. I don't find them particularly helpful. I agree though that bad dialogue when heard is a good way to learn what not to do.

Yeah.. they do need to improve the voices

Is it just me, or did the OP's message disappear?

Yes, that's weird.
Marty, come back and repost!

Yeah, now it looks like I started the thread and rambled to myself  

Quoted from Matthew Taylor Yeah, now it looks like I started the thread and rambled to myself

Yeah, you really need to stop doing that.  

I always knew Matthew was a little off

On the subject, I’ve tried everything from reading it aloud, reading it silent, or reading both characters speaking. All of which are decent methods, I guess. But my rule of thumb is usually the less said the better. Keep it concise and to the point. But. Do like reading it aloud and kind of acting it out. Seems to help.

Quoted from SAC I always knew Matthew was a little off

Only a little? I'll take that as a compliment  

A couple of things I do to try and help on the dialogue is:

1.  Listen to other people's conversations in real life.  If you're a good listener, that can help in carrying over into your work.  Of course, if you only hang around people that talk like robots, then I don't know what to tell you.

2.  Try to remove as much expository talk as possible from the dialogue.  If you have someone explaining what's happening, or why something happened, that's typically not the best use of dialogue.  Sometimes it can't be helped. But as a rule of thumb, skip the exposition.

Anyway, just spit balling.  Also, I wish the Final Draft reader was much more natural.  It's a shock to me that with technology being the way it is, Final Draft hasn't figured out a way to incorporate a natural sounding voice into their system.