I recommend making both an iTunes (computer) backup and an iCloud backup. That way if one fails you can try the other. Most things will restore through either backup. iTunes is usually faster, but more complicated in that there are more steps in the process, and if you interrupt that process some content won't be restored {at which point you can just try again}
iCloud is slower, but seems more thorough. It also tends to recover from interruptions when restoring apps. A few device restarts are commonly needed to kickstart paused app that have failed to download; but that's it.
It is always best to copy any important files, photos, or documents to another place before doing a restore. They will probably come back with the backup, but nothing is ever guaranteed. There are lots of online places you can copy your photos to, or just copy them to the computer.
Go through all your apps and make sure you know where any documents (if any) are stored, and make copies if necessary.
Here are apple's instructions on how to do a restore. Note that the bottom has links to how a backup is done as well.
https://support.apple.com/en-us/HT204184
No restore is 100%. Some games just don't backup their progress. Some apps just don't backup their settings. For iCloud backups you can turn on/off backups for most apps. It would be a good idea to check these setting out before the backup.
Settings > iCloud > Storage > Manage Storage > This iPad (under BACKUPS).