For this post, I thought I'd look at what your characters would wish for. Okay a lot is going to depend on your story, genre, etc but some general pointers I think would cross all of that and be true for most of them. These then are:-
1. To be well thought out before my writer puts me to paper or screen
I've found outlining a character to be a useful tool. I don't put down every single thing but I need to know their major traits, what might send them "over the edge", what drives them etc. By the time I've thought about all of that, I can hear the voice of that character and once I've got that, I can write them into existence! I've found that time spent initially in thinking about what I need to know here has saved me time later in editing and not having weaknesses in characterisation and/or the plot. The lovely thing here is each writer can decide what they need to know. It will vary from writer to writer. It can vary from story to story too. For example if you know you are going to write a humorous tale, you can ask what would your character dread happening to them because they'd be so embarrassed? There would be a lot of humour potential there!
2. To give me dialogue I can actually speak and which doesn't sound like "authorese".
This is where reading your work out loud pays off. You can literally hear if the words flow or not. If you stumble over dialogue, a reader will too. Time to edit then! Speech itself, as well as speech patterns of characters, must seem natural. You want to convey that this is something a "real" person in these circumstances might actually say (even if the setting is fantastical).
3. For the writer to know what they are doing!
We're back to outlining again. Your characters need to have a function to justify their place in your story. So you really do need to know what they are doing in your story and, as importantly, why. Once you know that, you can write with confidence (and it does show through).