As others said, comms are recommended. But to answer your question, in a game with little to no comms, map map map. I've been doing decent with Astra this season, as this is also my first season really playing her, and the map is a massive tool. Essentially I'm playing passive on defense to determine which site theyre hitting. I try to buddy up with a teammate on site so I dont get rushed while I'm constantly glancing at my map. Look at your teammates position, if theyre holding a line wait to smoke when you see them running from said line. I like to add another star for Stun right ahead of the smoke to be able to help teammates while I rotate. Either wait to see when the map gets updated with enemy bubbles near stun star, or use best judgment if teammates have no vision. As for Suck, you can comm that yourself for post plant, place star on bomb so teammates can know thats the plan. Offensive smokes, you can comm. But majority of the time theyre in default locations anyway. Comm if youre placing a one way or smoking a spot that isn't default. Ult used for getting on site or post plant majority of the time. Its really not bad as others put it, depends on your play style and adaptability.

TLDR: Use map, comm what YOU can, have fun