Shooting in a direction where you don't have the "light domes" of urban light pollution certainly helps.
You can use websites such as:
cleardarksky.com
clearoutside.com
To check local sky conditions w.r.t. cloud cover, transparency, seeing conditions, etc.
BTW, "seeing conditions" is a term astronomers use to describe the stability of the atmosphere. The best analogy I've come across is the following... suppose you have a pool and you've placed a coin in the bottom of the pool. I had you some binoculars or a telescope and ask you to use it to read the year stamped on the coin. If nobody is making any waves in the pool and the water is absolutely still, then you can probably do it. But if I start making lots of waves in the pool while you try to read the date, you might still be able to tell that there is a coin at the bottom of the pool, but you almost certainly will not be able to read the date. The atmosphere really does work like that pool. Some nights when the seeing conditions are great, I can see amazing amounts of detail... and sometimes nothing will come to sharp focus (as if there is something wrong with the optics on the telescope -- even though it's really a problem with the atmosphere.)
"Seeing" really impacts detail on a very small scale... things that are so tiny that I need to resolve detail on the scale of a few arc-seconds or arc-minutes. When we get to large scale structures it won't be so noticeable. This is why the moon usually looks pretty good (the moon is roughly 30 arc-minutes from edge to edge), but planets are tiny and it's a much bigger issue. (Jupiter's angular width from edge to edge is currently 43 arc-seconds... less than 3/4 of an arc-minute. That means you could line up more than 40 "jupiters" from edge-to-edge in the width of the moon. Tiny amounts of atmospheric distortion will have a much more noticeable and adverse effects on the clarity of small structures (or more accurately, things that seem like small structures because their "angular" size is tiny -- even if the real object is enormous). One other things... wind on the ground is not necessarily an indication of a stable atmosphere. I've had clam days at ground level with lousy seeing. Ideally one would be in a location where the surface of the earth is flat (smooth laminar airflow without geographic creating turbulent air), and you would be at least 200 miles from the jet stream, any warm front, or any cold front.
When using an ultra-wide angle lens, the effects of seeing will not be very adverse on your images.
Moisture, dust, etc. in the atmosphere effect "transparency". The biggest problem with transparency is that when you're near sources of urban light pollution, all those lights have something hanging in the air to light up. A sky with no dust and no moisture in it will be much clearer and there aren't lots of tiny particles that reflect light from urban light pollution. So the sky will seem darker when the atmosphere is clear. This is a big deal for astrophotography because much of what we are trying to detect are faint gray patches of light. If the whole sky background is a faint gray (due to light pollution and poor transparency) then those details won't show up.
You don't want any moonlight in the sky because that will add light pollution and reduce contrast. Check your calendar and plan to shoot when it's near the "new moon" or even the "3rd quarter" moon (because the third quarter moon doesn't rise until a few hours before sunrise -- so it won't be in the sky after sunset and you'll have hours to work.)
The part of the Milky Way that faces the center of the galaxy (the direction of the constellation Sagittarius) is the most dramatic. The part that faces away (mostly what we see after sunset in the winter months) is much less dramatic (that's facing the direction going toward the outer edge of the galaxy). If you get up in the pre-dawn hours (but now you want to shoot at a 1st quarter or new moon -- not 3rd quarter) then you get a preview of the skies in the coming months and the summer Milky Way will be rising. Unfortunately right now it's rising so close to sunrise that by the time it's really "up" you're probably betting some pre-dawn twilight interfering with the image. Each month the rise & set times shift forward by 2 hours. At around 4am in April you can catch the "summer" Milky Way rising high enough to be dramatic. In May it's even better.
