I think this largely depends on where in their career they are and how familiar they are with coding in the environment they just found themselves in (large org, small company, startup, tech stack, etc).
In general I find pairing a new hire with a less senior but relatively new hire to be a good way to get them ramped up quickly. Ideally this person has recently gone through the same process and can help get the new person unstuck. It also very much helps in the first few weeks to have a single point of contact to ask all the basic questions to get them up to speed before they feel comfortable reaching out to the larger org.
After this its all about knowledge transfer and task management. Helping them understand why things are the way they are, not just how. There is a tendency for new devs to come in and want to change everything to be "better" without understanding the reasons for the current state of the world.
Once they are up and running, giving them larger and larger tasks with less and less guidance will get them out of their comfort zone and needing to get better integrated into the team. They will need to ask for help from an area expert, sync with PM, and be responsible for something end to end (though likely already pre-defined by someone more senior).
If they've made it past that point they should start becoming more autonomous and a great candidate to be a mentor for new devs coming in. Once they hit this stage, I find giving them more responsibility and less guidance can help them grow, fail, and learn.
I could write a lot more about this subject but thats a general idea of how I look at the ramp up process. Getting to Senior is a whole different topic, but for context I've only ever worked at large tech firms so thats the only definition of Senior I know.
In general I find pairing a new hire with a less senior but relatively new hire to be a good way to get them ramped up quickly. Ideally this person has recently gone through the same process and can help get the new person unstuck. It also very much helps in the first few weeks to have a single point of contact to ask all the basic questions to get them up to speed before they feel comfortable reaching out to the larger org.
After this its all about knowledge transfer and task management. Helping them understand why things are the way they are, not just how. There is a tendency for new devs to come in and want to change everything to be "better" without understanding the reasons for the current state of the world.
Once they are up and running, giving them larger and larger tasks with less and less guidance will get them out of their comfort zone and needing to get better integrated into the team. They will need to ask for help from an area expert, sync with PM, and be responsible for something end to end (though likely already pre-defined by someone more senior).
If they've made it past that point they should start becoming more autonomous and a great candidate to be a mentor for new devs coming in. Once they hit this stage, I find giving them more responsibility and less guidance can help them grow, fail, and learn.
I could write a lot more about this subject but thats a general idea of how I look at the ramp up process. Getting to Senior is a whole different topic, but for context I've only ever worked at large tech firms so thats the only definition of Senior I know.