The first line of every paragraph should be indented. You can do this very easily if you use Word. Go to Format, then Paragraph. There's a box marked Special, which is probably empty. Click on the little arrow on the side and First Line comes up. Save this page. From now on, every time you press the carriage return key your next line will be automatically indented. Hooray!
Spaces between paragraphs
Academic formatting is no indents, and a space between each paragraph. Creative writing is just the opposite. You should only have a space between paragraphs when you want to indicated a new scene.
Sometimes Word randomly adds spaces between lines. Actually, it's not random, you need to go back to Format then Paragraph and check that the gap between lines is left blank.
When the writing is made to form a straight edge on the right as well as the left hand side. It makes manuscripts look like a block of text which can be off-putting.
Dialogue on completely separate lines to the speaker's actions
Character A does X (an action). Character A says something. It's on the same line. It's not:
Character A does X.
Character A says Y
Character B does Z
Character B says W.
Italics and other difficult to read fonts
Arial is supposed to be the easiest font to read, Times New Roman the most common. Choosing an unusual and exciting font will not make your work unusual and exciting, just harder to read.
It's a real pleasure to pick up a manuscript and realise it's beautifully presented. I want it to read well. Isn't that how you want an agent to feel when they pick up your manuscript?