When Selecting a Bug Bounty engagement to participate in there are many aspects of which to take into consideration. Some of those factors to be considered are:
Popularity of Engagement.
When selecting an engagement considering the engagement popularity is important, a bug hunter will want to consider how many other testers are actively testing an application, the amount of bugs that have already been submitted, the skill set required to find new bugs, the amount of automated testing platforms that have already been engaged with the platform. There are definitely other reasons to consider the popularity of the application but there are a few.
The Available scope of engagement.
When a bug hunter is inspecting the scope, some of the questions that may come to mind are, what are the types of endpoints that are in-scope(e.g. is there a web application, are there api endpoints, do they have any mobile applications, are there wildcard domains?) if a bug hunter is more proficient with finding web application vulnerabilities, then focusing on engagements that only have a apple mobile app, that way not be the engagement for that bug hunter.
What are the tools you'll need.
As a beginner bug hunter the question may arise, "what should I be using to test for bugs." Although there are a large swatch of application available to try testing applications, some do stand above the rest. Though i won't say which tools to use, i will say, OWASP has an amazing repository of tools for testing different applications, and different bugs along with great user guides and so many other resources. Also some other companies with great resource would be Bugcrowd, HackOne, nmap, burp suite, the Kali Linux organization, offensive security, and many others.
So Where do I Start?
I would say I start and stop all the time with bug hunting, and restarting has it's own complications similar to staring. Some of the First steps is deciding which engagment platform to sign up with, and at this time there are quite a few, weather that's BugCrowd, or Hackerone, Hackenproof, Immunefi, etc. I would honestly say I don't know that it matters which one you choose, other than aligning with what sector you want to take part in, i would say if you are looking for General engagements across multiple sectors that have a good bank of available engagements, Hackerone seems to have a larger list of large scoped engagements,
and i also like their engagement introduction programs, they let you test your skills and even have suggestive engagements based on skill sets. If you are looking to explore the web3 or opensource world of engagements please do your research and verify that the engagement you are participating in is genuine and legitimate, I will say immunefi is a solid platform with good organization. no matter what platform you choose to use be sure to read the terms of engagements and scopes very carefully and if you aren't sure, all the platforms have a good support system and engagement resources are always available.
Further Learning
I will once again site a hackerone product, they introduced hacker101, a program for learning the process of hacking with a good introduction on how to hack different types of applications and how to interact with the hackerone platform, and how to submit a good report.