For reading purposes, stick to a good, well-known serif font (like Times New Roman), or slab serif font (like Courier). The reason I say this is because - regardless of your manuscript looking like it was written with a typewriter font - serif fonts are much easier to read in print than sans-serif fonts (like Arial).
On a writing course I've done, they gave the following recommendations as well:
Definitely stick with the double spacing of your lines. Use a new line for paragraphs rather than a spaced gap i.e. the spacing between the previous paragraph and the new one is the same as your line height. Indent each paragraph / new line, except the opening paragraph of the chapter/section.
I'd also recommend using single quotes for speech, rather than double quotes.
Edit: Note that these are likely UK-based styles, particularly the single quotes.