For context, I've played nearly 10 games (some 1000, some 2000) since 10th dropped and I've played my friends who are of varying skills levels and armies along with myself playing Sisters, Aeldari, Chaos Knights and CSM to see what I like and just use what I paint. Despite this I've lost every game, ending up getting tabled around turn 3. Is there any specific advice I can get to increase my chances of having a fun fight without getting one-sided tabled?

A couple examples are World Eaters completely demolishing my sisters due to advance and charge and crazy melee, and my friend who plays guard often uses 6 tanks/vehicles that indirect and direct fire me down before I can get close or kill them back due to being tucked away and having so many vehicles that I die no matter what. It's probably just a skill issue but its been really discouraging and has sapped some of the fun out of playing and painting having lost 7 times in a row. Any advice or pointers to where I could learn more would be appreciated.