Applying the Zero-Product Rule to Everything
The zero product rule is what allows you to solve an equation like (x+2)(x-3)=0. By realizing that the only way two things can multiply to give us zero is if one or both are zero, we can say x+2=0 and x-3=0. This is all based on the fact that there is a zero on the right hand side!
If instead, we had (x+2)(x-3)=2 we couldn’t immediately take this approach. This does not imply that x+2=2 and x-3=2. Again, you can only apply this if you manage to get a product of terms equal to zero. (to solve the new equation, you could foil the left hand side and then bring the two over – going from there)
There are plenty of other mistakes that I have seen but these are by far the most common. In the end, it comes down to applying properties in situations where they do not apply. Learn to ask yourself if the rule you are applying makes sense in a given situation and you will be well on your way to avoiding these!