The Umbraco upgrade process has vastly improved over the years. However, there are still some steps you can take to ensure that your upgrades go smoothly.
This might sound like obvious advice, but you need to plan your upgrades and updates so your live website isn’t affected. My tips would be to upgrade a copy of your website locally. If you have the budget then load balancers can take a lot of the pressure off of your upgrade process. You can do the upgrade on an offline mode until you’re happy with it, then switch it live when it’s up and running. If your budget doesn’t stretch to more than one server, then your best bet is doing the release when you have the lowest traffic, usually out of business hours or weekends, but it depends on your particular site’s traffic patterns.
Upgrades can go wrong, and if you don’t back-up you can waste hours/days trying to get your site up and running, so before you attempt anything back everything up, database, webroot etc.. After doing that you’re ready to get going…