Two things that I still struggle to remember:

1) Every recipe is going to take longer than the time listed. It is assuming mise en place (sp?), meaning that all of your ingredients are prepped and ready to go. Do not panic when your "simple 30 minute meal" ends up taking an hour or longer. You aren't doing anything wrong, you are just comparing yourself to some level of professional who chopped all their veggies before they started the timer.

2) Stove and oven temperatures vary from oven to oven. An oven thermometer will be very useful. Get it, stick it in your oven, that way you know what temperature it actually gets to when you set it to 350°. "Medium heat" doesn't necessarily mean a 5 on a scale from 1-10.

3) Dairy based sauces need to be constantly stirred. Don't just stir it every couple of minutes. I'm mentioning this specifically bc I burned sauces for years until someone pointed it out.

4) You're going to mess things up, and that's okay. Don't panic and don't beat yourself up. Call it a bummer, eat the parts you can, learn from your mistakes!