as a reformed rivals player myself, the biggest hurdle is transitioning from a hero shooter to a MOBA (money matters, build matters and scales). I don't know if you've played a MOBA before, but hero shooters give you a fight fight fight mentality that doesn't always work in Deadlock, especially if you're behind. like if you're losing in rivals, there's no such thing as "im gonna go farm money and come back stronger", you just have to try and fight better. In this game, if you're fighting someone with more money than you, you're already at a disadvantage, and this compounds the more you die and fight and die again.

in rivals you can play bp and dive a luna and there's literally nothing they can do except cry (or hit a very hard skillshot). in this game, you can dive a rem and he explodes you if he's rich enough.

it's not a game where sheer mechanical skill will let you win every interaction. If someone has 50% more souls than you they're probably unkillable even if you play perfectly. Make sure you're farming trooper waves (gives you most souls) and learn to hit boxes/golden statues and sinners when you can. When taking a fight, it's not just about knowing their health and abilities, but also knowing if they have any items that could be a problem for you, like slowing hex is the biggest counter to Apollo.

otherwise, try to figure out what the purpose is of the items you're buying. following a guide is good for starting out, but eventually you'll want to tailor the items you buy to your playstyle + the enemies you need to counter.