Hilchos Shabbos issues that I’ve seen come up:
1. I’ve seen people cut up vegetables several hours before the seudah.
2.Many people don’t know the halachos of heating things up on Shabbos. I recently saw someone about to heat something up on Shabbos in a way that was a problem, but I stopped her in time. I had a sheilah once regarding whether or not I could eat something that was heated up incorrectly. (I also had to find out if it was in fact incorrect). Also, someone I know recently decided to start keeping food in her oven recently, so she had to find out if she was allowed to, and how.
3. I have a lot of questions regarding “Graf shel re’i”. I’m not sure if/when/how you are allowed to throw out things like empty wrappers and dirty tissues. I was once told that something I did was wrong, so I’m still trying to figure out what is ok and what’s not. I tried looking it up once in one of the Hilchos Shabbos sefarim, but couldn’t find it. And this comes up every Shabbos.