I kind of feel like fudging rules/rolls is kind of a more advanced GM technique. Like, breaking the rules to chase a storyline can be totally OK. In some systems, it may make the game much less interesting (like I play older D&D, and half the game revolves around both avoiding risky rolls by trying to talk or scam your way through something or else dealing with the fallout of a bad roll in as clever a way as possible). So like, figure out the system, first, would be my suggestion?
And like this is a reply to Wazanator too and I want to add that I don’t think this is bad advice or anything like that, I just think that sometimes for new people the inclination can be to fudge things so no one (maybe) dies or doesn’t get a storyline go their way or whatever and then accidentally you’ve removed part of the guts of the game.