A few things to consider - and you might already know all of it, but anyway...
Before the match, as the above poster says, it's common in the pre-match to talk about penalty decisions with (neutral) ARs. Something like "look at me first, am I already signalling no then follow my lead, or look at me to see if I want help... then, you need to be 1000% sure before flagging a penalty, and consider if are you credible... is it a breakaway challenge that I cannot see, is it a handball on your side of the box... etc."
Bonus, if you don't have headsets (not advised when starting out) then you can also talk with ARs' about showing "was it in or out of the box" when there is a foul and possible penalty. Switched on ARs will turn subtly and face the goal line or half way line to show you immediately it is in or out - this can help you swiftly signal and communicate with players and "sell" a decision.
Positioning - at a breakaway, ideally avoid being directly behind the play. Sprint fast - don't wait, if you are gonna go, go! - and get an angle so you are not directly behind the players. Most challenges, grappling etc. are much harder to see from behind. And any decision will be more credible.
Signalling - as a ref, your "no" decisions are very important. If there's a challenge - where players are likely to appeal, like a penalty situation - and you decide it is fair, then "cutting the grass" is the universally accepted way to tell the players, the benches, the fans and your ARs that you are happy. Conversely, if you stare at your AR with your hands down by your sides, your AR will see you want help. Also, if it is not obvious, use your voice... "get up, fair for me, carry on..." whatever works for you.
A lot of this is timing. What you don't want is to signal no penalty only for your AR to start flagging. Good ARs with good timing avoid this - but you also have to be quick with your "no decision" communication. You need to lead.
Can you wait, then stop play, and then go to ask your AR if there was a foul? No.This will destroy the match, you will lose control and the players will go crazy. It is your AR's job in any situation to "give the referee relevant and timely information" - and with fouls/penalties, that means flagging the foul so that you can whistle to stop the game. If you don't whistle, or your AR doesn't flag and you don't whistle... then the game goes on. It's not on TV, you don't have VAR.