Is there any rule or truth about what should be planted where in the garden?
What Should Be Planted Where
Certified GKH Gardening Expert
As far as design goes, technically, no there is no rule. But as far as individual plants go, there are as different plants have different temp, water and light needs. For example, you would not want to plant cactus next to marsh marigolds as cacti need dry, warm, bright sun conditions while marsh marigolds like shade, lots of water and moderate temperatures.
The best thing you can do is examine the conditions of your garden space. What kind of light do you get in different spots (and this may vary greatly in even one garden), what are your summer and winter temps, how much rain do you get and how much water can you provide, how is the drainage in your soil.
Once you know all these things, you can locate plants that like those conditions and plant them in the right spots in your garden.