One: the mole ratio
Students read the coefficients in a balanced equation as amounts rather than as a ratio. Write the ratio out as a fraction with its units on it, every single time, until it stops being a decision and becomes something the hand does.
Two: the limiting reagent
The instinct is to work out which reactant there is less of. That is not the question. Convert both to moles of product and take the smaller answer — the reactant with the smaller mass is often the one in excess, which is why guessing fails here more than anywhere else.
Three: the unit that vanishes
Grams to moles to moles to grams is four conversions, and most lost marks are one of them written upside down. Carry the units through the arithmetic and a flipped step cancels into something that is visibly not grams.
After that it is long division
Once those three are automatic the rest is arithmetic. Students who believe they are bad at chemistry are usually bad at one of the three above, and that is a fortnight of work rather than a subject.