I don't want to use for 'sh*t' and 'f**k' in my work. What else can I use that gives similar meaning?
Many stories have relied upon "in-world" curses, while others have simply used words from another language or those so obscure that they have less bite.
In-world: In Battlestar Galactica, the term 'frack' is used. It's close enough that it implies f**k without saying it.
Other language/Obscure: Firefly is the king here, using both many extremely offensive Chinese curses and a few obscure terms. Their use of the word 'ruttin' is synonymous for f**king while the term is in the middle-ground between common enough to be known and rare enough to be sterile.
Specific options of each would depend on the mood and setting of the story.
It depends why you don't want to use them.
If it's because of the intended audience, what works best for them? This will give you options like the "in universe" words others have mentioned or (as was common in children's comics) a string of normally unassociated characters (asterisks, exclamation marks etc.).
If it's because the narrator wants to express disapproval of something a character has said - a narrator with a strong character themselves - you could describe the words and let the reader figure them out. Umberto Eco did this nicely in The Name Of The Rose where the narrator (Adso of Melk) described William of Baskerville as using "a word in his own language" which "had an obscene hissing sound".
Sometimes not using such language is best. Harrison Ford is famous for using expressions without saying a word. I have found that readers aren't dumb and usually have a quick grasp for situations requiring such language. So, I would say not to use such language unless your character demands it. IF your character demands it, use the more forceful expletives.
I know some of these have been said but: What about “son of a bitch” “damn” “hell” “dag” “drat” “dang” “frick” “crikey” LoL “mf” “wtf” “mother trucker” “son of a biscuit” “jfc” “wtf/wtff” “fu” “eff me” smd” I think you get the point