ju - adverb of emphasis

There is nothing like the adverb ju in English. You can place it next to any verb to add emphasis to the statement, while also changing the tone of the statement. Depending on the context, it either means “as you know”, reminding of something that is known by both speaker and listener, or it expresses astonishment at new information.

You can also say ju X desto Y”, which means “the X, the Y” as in “the bigger, the better”.

Här är ju nycklarna! - Here the keys are! (Found them)
nycklarna är ju här - as you know, the keys are here
det här går ju inte bra - as you see, this is not going well
jag är ju inte dum - as you should know, I’m not stupid
ju tidigare desto bättre - the earlier the better