Keep all texts in the same size and to make it easy to read the fonts. You can make the texts size larger for headings or make it stand out by underlining or in bold. Standard text sizes are 11 or 12.
Do not use colourful fonts as your main text on the CV. It will be hard to read so use the standard black colour for your text.
CVs should be a about two to four pages (depending on your work experience). However, do not make it too long. Inserting page numbers will help too.