This blog post was prepared in 2014 and has links to items you might want to check out.
What you need to know about the concrete layer below your screed.  A properly prepared base will make a big difference to a sound and durable screed floor.  Remember, the preparation is different for an unbounded floor and a bonded floor

• Screeding 101: https://www.screedscientist.com/the-difference-between-concrete-and-screed/
• Surface Accuracy of Floor Bases: https://www.screedscientist.com/floor-screeding/how-important-is-the-surface-accuracy-of-floor-bases/
• An Unbonded floor https://www.screedscientist.com/floor-screeding/screed-constructions/unbonded-v4lr/
• Preparing your concrete for an unbounded floor: https://www.screedscientist.com/the-importance-of-flatness-of-concrete-substrates-for-the-installation-of-unbonded-screeds/
• Thermal insulation:  https://www.screedscientist.com/installation-of-rigid-floor-insulation-on-ground-floor-concrete-substrates-to-receive-screed/
• Preparing the concrete for bonded floor, including moisture testing: https://www.screedscientist.com/how-to-prepare-the-floor-substrate-for-levelling-screeds-and-toppings/