A first draft should have neither too much nor too little importance attached to it. It is a place to work out ideas and explore your story’s potential, but it is generally not the right place to worry about rewrites or line edits.
Writers approach first drafts in a number of different ways. Very few writers produce polished first drafts, and the ones who do tend to be experienced authors. However, even most experienced writers extensively rewrite and revise their first drafts.
The way that you approach your first draft will differ depending on whether or not you plan and outline ahead of time or whether you prefer to learn about your novel while you are writing it. Some writers who do the latter refer to the first draft as the “discovery draft” meaning that their first drafts may be even more unformed than a typical first draft. Discovery drafts may combine elements of the outline with the first draft in that some sections may be left unwritten with simply a few notes about what happens, but they also contain substantial sections of prose and approach the length of a regular first draft.
For writers who outline heavily in advance, the first draft can be an opportunity to test the strength of that outline. Most writers who use this approach usually find that some aspects of their plan do not work. It’s best to avoid sticking too rigidly to the original outline at this stage as new ideas reveal themselves. For these types of writers, the first draft is the place to begin testing the plot and characters as originally envisioned.
Between these two extremes will be writers who do a little bit of planning and write fairly substantial first drafts. Along with discovery draft writers, these types of writers may benefit from outlining as they go along. Having a separate document that breaks down scenes and their purposes can help you with structure when you go back to revise.
In addition to figuring out what sort of first-draft writer you are, you should also think about whether you would like your writing critiqued at this stage. Some writers benefit from having readers look over their novels at this point while others would be paralysed by a critique this early on in the writing process. If you feel like you’ve done all the work you can on your own on higher-order issues like plot and characterisation, you may find feedback helpful at this stage to see how effective those elements are. However, if in reading over your first draft, you see a number of places where you could improve those elements or if you are planning to make substantial changes overall in the next draft, you should probably hold off before getting others to read your book and make suggestions.
To some degree, first drafts should be exactly what you need them to be. There are not too many first-draft don’ts beyond the fact that you need to avoid getting bogged down in going back for rewrites. Endlessly rewriting the first few chapters or first few dozen pages is one of the biggest dangers for the beginning writer.