Then look in the compendium for a class combination that you think will be fun to play, easy to gear and powerful. I.e. try to stay out of g5 tags and also if char has Conduit amulet with build enabling affix.
Then look around for beginner/budget guides which will at least get you going some basic farming.
For instance, warlords, paladins, dervish, infiltrators etc will kinda “always” be good for high endgame stuff.
Even if a char you have now can’t do c+ and sr+, you can at least start doing basic farming with it so that leveling and gearing up other future chars faster and smoother. I.e. most of my budget builds can farm challenger crucible and elite shattered realm as they are presented basically and you can soon swim in gear. By planning for future chars, you know what items to look for now, what to keep, what rolls on green and MI’s are worth keeping and so on
Also, be aware of patches… they can either bless or curse you
btw these tags are just an arbitrary forum standard, you make your own goals about what your chars should be able to do and how you approach the game. Grim Dawn is not Diablo 3 or PoE you know …