As someone accustomed to Microsoft Word, getting accustomed to formatting term papers in LibreOffice was a little counterintuitive. This is a little crib sheet I put together a couple of semesters ago; LibreOffice is both wonderful and terrible.
1. Consult the OWL.
2. Normal 12-point font.
It's easy to select all text and change the type face and size in the pulldown menu on the main editing window. Also click the 'Format' menu item, select 'Paragraph…', then under 'Spacing' set 'Above paragraph' and 'Below paragraph' to '0'.
A more permanent solution is to change the styles, which will make this the default for every new document. Click the 'Format' menu item and select 'Styles and Formatting' (T). In the popup menu, make sure the highlight the 'Paragraph Styles' icon is highlighted, then right-click 'Default' and select 'Modify…'. Click the 'Indents & Spacing' and 'Font' tabs at the top, then change the settings and click 'OK'.
2. One-inch margin.
The easiest way is to select all text, click the 'Format' menu item, and select 'Page…". In the pop-up menu, set all the margins to '1"'.
Editing the 'Page Styles' doesn't change the default. Apparently you have to open the template "Default.ott" to edit, make the change above, and save the file, but I haven't managed to do this yet.
3. Half-inch tab stops.
Click the 'LibreOffice' menu item and select 'Preferences…' (,). In the menu, select 'LibreOffice Writer', then 'General', which opens the panel that allows you to set the tab stops to 0.50".
3. Running header.
Click the 'Insert' menu item and select 'Header >' then 'All'. Put the cursor in the header, hit Tab twice, and type your last name. Click the 'Insert' menu item and select 'Fields >' then 'Page Number'. This puts the header on every page.
To then remove the header from the first page, put the cursor in the first page. On the status bar, click "Default" and select "More…" This brings up the "Styles and Formatting" window. Select the "Page Styles" tab and select "First Page". This applies a new page style to the first page, removing the header from that page. Close the "Styles and Formatting" window. IIRC, this re-sets the margins to the default, so you'll have to change those again too.