It's easy for Switzerland: They have no ß.
In capitalized words, the ß is usually replaced by a double-S (but see edit and end of answer). There are very few fonts featuring a capital ß, and there's no direct way to type it. Most germans don't know it exists.
Please note that an ß is not simply two s after one another, it's a different character, which is why Bundes|straße can never have an ß at the end of Bundes.
Words never start with an ß.
An ß is always sharp, not vocalized (like the english s in ass, unlike the german s, which is very often pronounced like the z in lazy).
Whether or not you use an ß is usually determined by the length of the vowel preceding the s/ß: You never have an ß after a short vowel. For example, muß (must) used to be correct, but since '96, it's muss. Muße (leisure) has a long vowel, so it has an ß.
The ß is also usually found after a diphthong, as in beißen. Probably because diphthongs are usually also long.
EDIT: The capital ß (Versal-ß in German) is slowly gaining popularity since it has been adopted as an actual letter in Germany (without much fanfare). It had been part of the Unicode standard since 2008. Still, many fonts don't include it.
Here are some examples: Straße/STRAẞE/STRASSE Straße/STRAẞE/STRASSE
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Even though I really welcome it, it still looks strange to me.