I always try and break down my match into mini goals to help migitate nerves, giving yourself something smaller to focus on, instead of stressing about the win.
Like first stock, i always think 'ill try to keep my opponent on more % than me'
as we get near kill %, i focus on being more careful and not making a mistake.
If i get the kill and take the lead, i think to myself "try to get 30% on them before they kill me.
Then if i get that, i stretch it to another 30%.
After that i try and land a charge shot, and all of a sudden i find myself with a 85% lead, and they're off stage.
I just keep the mini-goals coming, to make sure i'm on track, feeling like you achieve something like getting 60% on for a stock lead mitigates the feel of a loss of stock when they do kill you, so you can keep positive.
Maybe that holds more for samus, because if i get a stock lead, bunkering down is a legit strat. As opponents can easily take 50-60% fishing for a kill when they get impatient vs samus.