I have been doing work outs for 8 days consistently.

to do a work-out, or to do work-outs, says you were doing specific exercises all together. you could also say simply you have been working out, which means you were exercising in general. the difference in meaning is pretty much non-existant, i just wanted to add it because i would personally say the latter.

also - 8 is more than 1, so day becomes plural. but i think that was maybe just a typo.

Not only for keeping fit but for keeping mentally healthily, I’d better raiseget up early and keep daily exerciseing daily.

this technically is not a complete sentence, it should be joined with the previous one and cut off at the comma:

It makes me feel really good, not only for keeping fit but for keeping mentally healthy. I'd better get up early and keep exercising daily.

when you say you're "keeping mentally healthy," you're basically saying "keeping healthy." but you mean specifically your mental health, so you have to add "mental." healthy is an adjective (describing you!) so mental can't also be an adjective. (adjectives describe nouns, not other adjectives.) an adverb can be used to describe an adjective, so mental becomes mentally.

"raise" isn't a word we use to refer to waking up. you could say "rise," but it sounds a bit odd.

He suggested to us to use his methods, like four -words exercises, variations, and full paragraph variations.

when you suggest something, the object is the thing being recommended/encouraged. so he isn't suggesting you, he's suggesting his methods. so, "us" is the indirect object, and you must use "to" to indicate that.

so it's: He (subject) suggested (verb) to us (ind. object) to use his methods (direct object).

oh isn't english grammar so fun? :,)

for the rest - i'm not sure what "variations" is supposed to mean here so i can't rewrite it :v but i'm assuming there were multiple exercises using 4 words, so i made that plural. and the whole phrase four-word is kind of acting as an adjective to "exercises," so i wouldn't make "words" plural there. i wrote a dash between them to show that they're kind of working together to be an adjective. the dash itself would really be optional though.

Hope I can stick to doing these practices so that I can form the habit of using words, not just stop at knowing that word.?

technically you should have the word I at the beginning of this sentence, but i am extremely guilty of omitting subjects in casual writing so i won't fault you for it lol

i replaced the bit i didn't understand with a ? because I'm not sure what you mean to say, and it makes the bit before it confusing as well. you want to form the habit of using new words? using familiar words more quickly? do you mean you want to not have to stop at words you don't know? or do you mean you want to like fully grasp English and not just memorize the words but integrate them into your language?

However, these exercises are challenging because I have to think over and over again that if I should put this or that word in the sentence i, if it's right, and if it sounds natural.

it's one thing to start a sentence without "I" but you can't really do it mid-sentence

every other phrase in that list began with "if" so i made the "is it right" part begin with "if" too.

you could technically just write "if I put this or that", but I think "should" sounds more natural. also, about sounding more natural, i think most people would say "this word or that word"