Well, Jayce isn't the best in a lot of 1v1 match ups, you have to poke the enemy down first. If they go back, good for you, free farm, if not, try to all in.
If they're impossible to kill just farm, Jayce is a beast mid/late game poking machine. (play few games with him! He's godly!)
And you can't do anything about the team, if they're bad or toxic, just report them I guess :/