I hate that soft sign. Why have a letter that doesn't have a sound? Well, no sound that my ears can detect, anyway. It plays havoc with my spelling.

But now I think I'm starting to guess where it will crop up. Patterns are emerging.

It will never be:
At the beginning of a word
After the prefix (though the hard sign might be)

It will always be at the end of:
An infinitive ending with -т
A reflexive ending with -с
A second person verb ending with -ш

If it wants to, it can appear:
At the end of a masc/fem noun (particularly ones ending in -т -л -н -с or -р)
In the middle of a word, between two consonants (look for -т -л -н -с or -р followed by a nice hard consonant like к).

Am I on the right lines?