1. in manners holds her still: politely keeps silent.

2. comments: elaborations.   compiled: composed.

3. Reserve their character with golden quill / And precious phrase by all the Muses fil'd: i.e., keep their character by being written with a golden pen and ingenious phraseology polished by all the Muses. —I believe that Shakespeare is sarcastically imitating the bombastic manner of other poets.

5. other: others.

6. unletter'd clerk: illiterate assistant to a priest.

10. most: utmost.

11. that: i.e., that which I add.   in my thought: i.e., silent.

12. before: i.e., before all others; in first place. —The "his" refers back to "love to you."

13. respect: take notice of; regard.

14. speaking in effect: having the same effect as speaking.