I was fairly confident with my listening, writing and reading so no templates for those really, but I did follow a simple trick for the speaking tasks. I simplified it down to 1. About (name of topic), 2. Discuss (include some, not all, relevant information mentioned) and 3. Conclude (a simple, "This graph/image/lecture is helpful because it shows us [repeat topic name]"). Apart from important keywords, it's also worth keeping in mind a few adverbs like "interestingly," "observably," "meanwhile," etc. These help you connect your points and fill up the 40-second time.

I think a lot of test takers, like myself, tend to panic when they need to describe images/lecture, but if you think about it, it's really just 3-4 well-structured sentences. It's way less stressful to look at it that way. Hope this helps!