A few short words tell how you do something and look like the describing word: fast, hard, late, early. With these, add -er to compare two, and -est for the top.
Short action words: -er / -est
Hiroshi runs faster than Lars.
Of everyone here, Amina works the hardest.
Lars arrived later than Mei.
Watch out for early: it ends in -y, so the y becomes ier: earlier, the earliest.
Careful: lately is a different word — it means recently, not late. He arrived late and He has been busy lately say different things.
Try it: Hiroshi runs ___ Lars. (faster than / more fast than / faster that) Answer: faster than — Fast is a short word, so add -er: faster (not "more fast"). And to compare two people, the word is than, not "that": faster than Lars.
Words ending in -ly: more / most
Many words for how end in -ly: quickly, slowly, carefully, clearly. These do not add -er. Use more to compare two, and most for the top.
Sofia speaks more clearly than her brother.
Please drive more slowly here.
Of all the guides, Mei explains the most carefully.
Try it: Sofia speaks ___ her brother. (more clearly than / clearlier than / more clear than) Answer: more clearly than — Clearly ends in -ly, so use more in front, not an -er ending (not "clearlier"). And keep the -ly word itself for how she speaks: more clearly than (not "more clear").
well, badly, far
A few have their own forms. For doing something well, use better and the best. For doing it badly, use worse and the worst. For distance, far → farther → the farthest (or further → the furthest).
Mei sings better than me.
I slept worse than usual last night.
Lars threw the ball the farthest (or the furthest) of all.
Try it: Mei sings ___ me. (better than / more well than / gooder than) Answer: better than — When you do something well, the compare form is better, not "more well". And "gooder" mixes it up with good. So: she sings better than me.
Try it: Of the whole team, Amina trained ___ and prepared ___ for the race. (the hardest … the most carefully / the most hard … the carefullest / the hardest … the carefullest) Answer: the hardest … the most carefully — For the top of a group, hard is short → the hardest. Carefully ends in -ly → the most carefully. A short word takes -est; an -ly word takes the most.