Here is a good set of basic, non-commercial how-tos and general advice on setting up at home and then setting off with your Apple iPad or similar tablet device although the screenshots are all iOS. This is basic information. If you are an experienced digital traveler, you already know most of this stuff and have your own opinions and practices. This simple advice is generally appropriate for phones and some notebooks, too.
Notes: This article does NOT include SIM/eSIM product reviews or recommendations for apps or service providers. As of the date I am posting this link, the article was up to date in August, 2019. There may be some post-Brexit or newer tech and OS issues that require additional research. WikiHow pages include tons of embedded ads, best to ignore them all.