Steps:

1. Get Servo building and running locally following project documentation at http://github.com/servo/servo.
2. Run ./mach cargo-clippy
3. Fix an issue by understanding what the error means and correcting the issue. For instance

warning: redundant field names in struct initialization
   --> components/remutex/lib.rs:168:13
    |
168 |             data: data,
    |             ^^^^^^^^^^ help: replace it with: `data`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_field_names
    = note: `#[warn(clippy::redundant_field_names)]` on by default

In this case `data: data` can just be replaced with `data`.

4. Open an pull request with your fix, filling out the template, and giving it a full name like the following "clippy: Fix a redundant field warning in components/remutex/lib.rs.
5. Include a link to this issue in your pull request description body.

As this issue is large enough to be worked on in parallel, please don't ask to assign it to yourself. If you want to post fixes for a particular section of code, just check the PRs linked here to make sure that you are fixing different issues.

NOTE: The warnings for missing safety documentation for unsafe code is already handled in PR #33748. Please ignore those.