This will vary based on the needs of your inhabitants, or your future inhabitants. I recommend researching the care (and parameters) of all your current and planned critters, and cater to their needs.

Temperature: some people will go for mid-high 70's. I stay around 81-84.
rapid swings is probably the biggest problem.

amonia and nitrite should be 0 once your tank has cycled.

nitrate should probably be <20 for the fish, and preferably <5 if you have sensative inverts (perhaps the corals you plan to get)

pH 8.0-8.5, stability is important.

specific gravity of 1.025-1.026

I recommend reading a good book or two on marine aquariums to get a foundation. It can help avoid making common mistakes, and also give you a basis to judge and filter through all the internet-based advice.