Here's what I would avoid when traveling to Poland:

• Zakopane, it's overpriced and very crowded. If you want to visit the area the town is in your better off staying in smaller villages, unless you have to use public transit.
• Szczecin --not an 'avoid at all cost' but more of a 'there are better cities to visit'-- this-or-that part of the city is always being remodeled/reconstructed and there's no 'old city' with day and night life focused between two shoping centers and some roundabouts in the city center. If you want to go sight-seeing Kraków, Wrocław or Gdańsk are much better choices.
• Mazury lake district, beautiful lakes and decent nightlife, shit infrastructure - roads are narrow (two bigger cars can't pass eachother without going offroad) and often lacking sings and other markings
• Podlaskie Voivodship, even worse infrastructure than Mazury, it's rural, mainly towns and villages with nothing a tourist might want to see. You might think it's a good place to go star-gazing but Bieszczady are a lot better for that (Tho you should probably go to a Dark Sky Site for that, there's one close to Bieszczady, in Slovakia)
• THE SEASIDE, it's crowded, expensive, the sea is cold and it's fumcking wimdy, go to like Italy, Croatia, Portugal or Spain instead

Also in general avoid capital cities, they are often the worst of major cites in a given country.