english is my first language and I’m often at a loss myself to understand the rules of spelling and grammar. the rules are variable partly because, like most english things, the language is mostly stolen. also, the language is evolving all the time because of international english usage, or decisions by newspaper editors.
to be honest, spell-check and auto-correct are sometimes the only way i know whether or not to use double consonants
however, here is an example of a rule from encyclopaedia britannica which might help you…
To know when to double the final consonant, follow the rules below.
RULES
In a word with 1 syllable, double the final consonant ONLY if the word ends in 1 vowel + 1 consonant.
In a word with 2 or more syllables, double the final consonant ONLY if the word ends in 1 vowel + 1 consonant AND the final syllable is stressed.
At the end of a word, don’t count w, x, or y as a consonant.
APPLYING THE RULES
These verbs get a doubled final consonant:
tip / He tipped the waiter. /He isn't tipping the waiter.
cram / The students crammed for the test. /The students were cramming for the test.
regret / Carl regretted the things he had said. /Carl was regretting the things he had said.
These verbs do not get a doubled final consonant:
vote --> voted, voting (vote ends in a vowel)
instruct --> instructed, instructing (instruct ends in 2 consonants)
listen --> listened, listening (listen has 2 syllables and the final syllable is not stressed)