One thing that people think about science fiction is that you have to be an expert in engineering and physics to write it. You don’t, you just need to know where the stoplights are are.
By stoplights I mean things you can’t do, or if you do you must do with forethought.
As for the laws of physics there are really only a handful you need to be wary off. This is not saying you can’t violate them, but if you do it will have a big impact on your setting and you should think about it.
The first of course is faster then light travel. I will say that technically are a few ways around this that do not violate the laws of physics, but they tend to require exotic matter (matter with negative mass) or something equally unlikely.
Also be aware that you would be hard pressed to find a way to go faster then light in the real universe that would not also work as a time machine.
The second of course is time travel. Violating causality is probably the first or second thing most scientists would say if you asked them for a list of impossible things. No plot element causes more problems, for the love of god if you use this think it out.
The third is conservation of energy and momentum. Also known as not getting something for nothing. If something is being powered, where does it get the power? If something is moving what pushed it?
You don’t have to do math but if you have a machine doing something think about the kind of power it uses and what that means. If you have a ship move half the speed of light that takes a lot of power, it does not matter what kind of drive system it uses.
Lastly try not to go against the grain of science. By this I mean make your fake science SOUND like real science. Science in its most basic form will be the same in a thousand years as it is now, the thought processes will be the same because we will still be studying the same thing (the universe).