How to avoid careless mathematical errors?

I found this discussion on reddit “How to avoid careless mathematical errors?“:

Hi //math.

I am a high school student who happens to be VERY good at math, but who consistently fails to get As on tests due to careless errors. Most of the time, they come from forgetting a 0 after a decimal place, multiplying instead of dividing, putting a decimal point in the wrong place, or just factoring wrong. I actually had to drop a Precalc Honors class because I got Ds on tests from the sheer number of stupid mistakes I made, despite understanding the material very well.

I assume that this occurs because I work quickly, but if I work slowly, I run out of time on the test. Additionally, my handwriting is horrible, but there’s really nothing I can do about that. And even when I check my answers after finishing, I still…