For starters, two amendments:
1) Term limits on SCOTUS. It's obvious that since the President appoints them, we don't want their terms to be too short, because then we'd be recycling Justices every time we recycle Presidents, which would lead to the SCOTUS always being under the control and agenda of whichever President is in office. We also don't want to make their terms too long, as there's no point in giving them term limits if it's almost their entire life to begin with. So, I would say one twelve year term is an appropriate term limit for SCOTUS.
2) Term limits on Congress. Like SCOTUS, we don't want to be recycling Congressmen/women every time we recycle Presidents, and we also don't want the Congress to have a minor two year or less term. So I would say we give Congress two six-year terms. That way they can outlast the President and have (about, if they are reelected for their second term) the same term period as SCOTUS.
Then I'd make an amendment making separation of church and state EXPLICIT, so we can stop all these arguments about what the meaning of "no" is. That amendment would also make it clear that it extends to the states, too.
I think that settles me for now.