どうせ

どうせ is an adverb meaning "anyway": the speaker treats the outcome as already settled, whatever anyone does. It goes at the start of the sentence or clause, and the rest is an ordinary plain or polite sentence, often ending in だろう or a negative.

The tone is resigned. The speaker has already given up on a better result.

"Since it's going to happen anyway"

With から or なら in the same sentence, the settled outcome becomes a reason: since it's happening anyway, you might as well make the most of it. This use is not gloomy. どうせ〜～なら takes the plain form before なら.

どうせ or とにかく

とにかく means "anyway" in the sense of "leaving that aside" and moves the talk on. どうせ means "anyway" in the sense of "the result won't change". They don't swap.

Usage notes

These go beyond plain resignation.

About yourself

With なんか after a word for yourself, どうせ runs yourself down.

About someone else

Said about the listener's plans or abilities, どうせ sounds dismissive. It belongs in casual speech, and in polite speech it is rude.