The sound "ch" makes in German is one of those that is difficult to produce for an English speaker, because it doesn't naturally occur in English. Here are a few pointers to help you figure out how to pronounce "ch" words.
1. Soft-"ch" after: i, e, ä, ü, ö, ei, ai, eu, äu
When "ch" appears after these letters, it will be pronounced "softly" (with your tongue pressed against your pallet a bit, and the sound coming from the front of your mouth)
"sch" is pronounced like the English "sh" sound, but careful, there are exceptions: When the letter combination "sch" appears because the "s" is the end of a syllable, and "ch" as the beginning of the next syllable, which is often the case when we use the diminutive suffix "chen" then the "ch" is soft: e.g. "Tässchen" (the little cup): "Täss" is the first syllable derived from "Tasse", and "chen" is the diminutive suffix.
Mensch (human), Tasche (bag), Schach (chess -> notice the hard-ch sound at the end, because it is preceded by "a")