Assuming all we want to use is GitHub, the best way does not exist but there are couple of alternatives used by folks around.

Regardless of the final installation method it is safe to say that it is beneficial to first have a .paclet file created (search around for PackPaclet) and, depending on the method, attached to a GitHub release.

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TLDR I am using the last one ([MPM](https://github.com/kubaPod/MPM))

# 1.1. install.m script

You can add an `install.m` script in your repository. User is supposed to call `Import @ "url/to/install.m"` and the installation procedure does whatever you want it to do.

- Examples:

 - https://github.com/kubaPod/MPM#installation

 - https://github.com/FeynCalc/feyncalc/wiki/Installation

- Pros:
 - flexible installation routine

- Cons:
 - ugly url to type by the user: ``https://raw.githubusercontent.com/`username`/`pacletName`/master/install.m``, sure it can be copied but the fewer steps the better.

# 1.2 ResourceFunction installation script

Presented in Szabolcs' MaTeX where the installation script is a `ResourceFunction`:

- Examples:
  - https://github.com/szhorvat/MaTeX#installation
  - [FEMAddOnsInstall](https://resources.wolframcloud.com/FunctionRepository/resources/FEMAddOnsInstall)

- Pros:
  - flexible installation routine
  - simple call e.g. `ResourceFunction["MyPacletInstall"]`

- Cons:
  - The resource function needs to be verified by WRI before it is available

# 2. GitHub hosted PacletSite

You just build .paclets to your repository and update PacletSite.info. 

- Example:

  - [Carl Woll's GraphicsInformation](https://mathematica.stackexchange.com/a/138907/5478)

- Pros:

  - once paclet site is added user can quickly check for updates etc.
  - all WRI built-in functions based deploy-release-install 

- Cons:

  - Adds a lot of weight to your repository since binary .paclets need to be kept there. For this reason probably not the best for large or frequently updated projects.



# 3. A paclet installation manager

The idea is to install a 'paclet manager' once and it should handle standard Github released packages. 

- Examples

  - MPM`

     I created a simple installation manager MPM`: https://github.com/kubaPod/MPM

     Once you install it (using install.m :)) you can just call `MPMInstall["szhorvat", "MaTeX"]`. Check more examples in the GitHub wiki or [this answer](https://mathematica.stackexchange.com/a/163680/5478)

            Import["https://raw.githubusercontent.com/kubapod/mpm/master/install.m"] (*only once*)
            Needs @ "MPM`"
            MPMInstall["kubapod", "devtools"]

  -  `PDInstallPaclet`

      Alternatively take a look at [b3m2a1's `PDInstallPaclet`](https://mathematica.stackexchange.com/q/152660/5478)


- Pros:

  - easy to use
  - full of utilities

- Cons:

  - you need to trust the source of the manager like MPM (otoh with plain text .m it is easy to inspect)
  - unless standards are expanded it only does paclet install and any fancy setup needs to be run separately