Firstly, it's a numbers game, so don't get down about rejection. You'll likely get a lot of it.

To stand out: Demonstrate an appreciation for communication, and generally the sort of things that are going to make life easier for your manager: Capacity to work independently, but ask questions when you're stuck. Demonstrate an interest in software maintainability and a capacity to contribute to existing projects in an effective way.

Tests, estimation, goal-orientedness, etc. From there, skills with the code are great, but I think you're mostly speaking to someone who doesn't want more work managing an intern. They need to know you're mature and self-driven.

I don‘t even look at the resume much, just digg a little through the cv and then i invite them for an online interview to get a feel for the candidate (this is of course not possible for a large company with hundreds of applications). What i am after in the interview is some sort of „fire“ for programming, sonething that tells me they really like to develop (sideprojects (this can be a script you did to automate a chore), talking passionately about a specific technology you find interesting, anything like that) and the second thing is if i think you suit the team/company, if you are nice, maybe a little cheeky and can hold a conversation, that‘s all i need