Students speak Spanish when saying something is easier than not saying it. That means three things in the room: a reason to talk that is an opinion rather than a fact, the words visible within arm's reach, and enough silence before the question that the first answer is a considered one. Every page that ranks for this phrase is describing some version of those three, except one, which takes points away for English instead.
We read all seven pages that hold the first page for "how to get students speaking Spanish in class," which is the softest phrase in our whole gate batch and is held almost entirely by individual profes. We kept their names on their ideas. The chat mats and projects at the bottom are ours, made for a K-12 Spanish room by a twenty-year Spanish teacher.
The target, and where it comes from
ACTFL recommends that language educators and their students use the target language as exclusively as possible, 90% and above, at all levels of instruction. That is the number these pages are all implicitly working toward, and it is worth stating because 90% is a very different goal from "speak more Spanish." It means the default language of the room is Spanish and English is the exception you have to justify, rather than the reverse.
Erin at The Spanish Brew is the only one who describes a whole lesson built to hit it: a bell ringer of two quick questions, calendar and weather talk, a picture talk on one interesting image with true or false comprehension checks, and then a guessing game built from the answers students gave in the bell ringer. Her note on delivery is the useful part. When she reveals who a clue is about, she stretches it out and acts surprised rather than stating it, because the stretching is where the repetitions come from.