WordPress – Backup
Manually backing up files is probably the safest way to look after your wordpress site as well as any customer you get. The reason is you have total control and your not relying on third party software.
I do this for my customers and a few times it has saved me and got me more business as I did not loose all the customers website when the back up software failed. This is what I call added value for my customers and is a selling point. I do it each and every month.
There are lots of plugins that will do backup for you also. If you have good hosting they will also do a full backup for you. We use one called Updraft https://wordpress.org/plugins/updraftplus/
What should you Backup?
Basically I use the same plugins and theme on each site so I have a folder with these. Secondly you need all the graphics, pdf etc and these are usually saved in uploads under WP Contents using ftp. The last part is the database with all your layouts etc. Create a customer folder for each project and save the uploads and database.
Now these are oldish videos I hunted out when I was upgrading my business and I still refer back to them today because like everyone I tend to love gadgets and make things to complicated.