NO DRAMA departures or arrivals - this is really key. No goodbye kisses or cuddles, just tuck your pup in and go without fan fair. When you return, don't go and immediately greet your dog or make a fuss over them, ignore them until they are calm and quiet - only then give them a nice pat on the head and continue about your business. The smaller the production you make about your comings and goings the better, the quicker your pup will learn it's not a big deal
Remove the POWER of CUES - randomly put on and take off your coat while you're in the house, carry your keys around in your pocket and jingle them, put your shoes on and take them off without leaving the house. This desensitizes them to these cues and helps to dissociate them with leaving.
Make alone time rewarding - toss some kibble into their blankets, give them a frozen peanut butter/ kibble Kong, try puzzle toys, save their favorite chew toy for when you leave...give them something something cognitively stimulating to enjoy, so their to busy to fret about what you are up to.
DON'T GIVE IN - we know this is tough when you hear your pup crying or you're worried about destruction, but if you given you are reinforcing the behavior, and teaching them that if they cry eventually someone will come let them out.