If you have SSH access on your host, you should be able to follow the official Flarum installation instructions.
You can also try Pockethold if you don't have SSH access. This one isn't guaranteed to work, but if it does you should be sitting pretty.
Some hosts may not have critical php modules enabled, or disable others that are necessary, so you may need to check with them if you encounter errors. There are so many different configurations for shared hosting that if you encounter a problem, it may be possible to diagnose and fix it, and it may just be that your shared host is incompatible.
