Note: This is more of an opinion post with a plane thrown in. if you find yourself in a couple of these categories, it doesnt mean you're bad, as some of these criticisms are aimed at high quality builds. These are also just my opinions which means they're automatically worse than terrible and worthless. That said, These are some things I see somewhat frequently that kinda make me roll my eyes a bit:

• Setting fuel or engine power to stupid high levels.
• setting dragScale=0 or massScale=0 on exterior/ non interior non decorative parts. these first two are a really cheap way to make your plane better but it doesnt teach you much about aviation or even the game physics engine.
• Setting dragscale=0 and NOT DISABLING Drag calculations. (Seriously, if youre gonna make your plane like this, at least spare us the computing power, especially on high part builds)
• spending an excessive amount of blocks and time designing something the game already designed for you (this is my first time trying out custom paneling and landing gear and its directly inferior to the stock parts, but people go crazy over having/ not having this stuff.)
• Putting a ton of weapons on the plane and making it take up the entire plane.
• posting the same plane several times in a row, especially in a short time frame or without any major changes (im guilty of this as well, feel free to point and laugh at me and call me a hippogriff or whatever)
  -asymetric drag/ part placement on symmetrical builds (this is a glitch rather than a builders fault, and ya hate to see it.)
  -floating parts (really, this shouldnt be a matter of being a newbie but just testing your creations. if you need help, use the help tag and someone will give free advice.)
  -Blocky creations (not shown here but its still a minor gripe). dont use the block parts, theyre bad for your cholesterol. use fuselage parts instead.

Theres probably other things but these are the major ones for me. if you do these, then it means you're either growing as a builder and can learn from these, or you're already super experienced and can/ will probably ignore this lol. but really, if theres one takeaway from this almost sh!tpost, its to take advantage of what the game is designed around: learning which design aspects will make your plane better or worse and getting creative. oh and making simple planes. high part builds require skill but so does being resourceful in making low part ones.

Oh also i've working on something, theyre pseudo- replicas of planes that represent different era's of aviation in terms of basic design and flight characteristics, made by Generic Aviation and its advanced development division Mundane Works (Which will be a few purely fictional designs that somewhat fit the time period). ill be releasing those hopefully soon.