The last thing you want to do for a good aquascape is throw everything in randomly
Most bodies of water have some flow, which tends to 'sort' things by size and weight, so heavy things get dropped where the flow is slowest, usually on the inside of a curve and nearer the banks, and lighter materials will end up where the flow is fastest; out in the centre of the stream or lake, and on the outsides of bends.
So, decide whether you want a fast flowing stream or a slow moving lake (this will mostly depend on your fish), and where the water would be coming in and going out, if your tank was a section of it.
Then you can clump your stuff together in a natural way
Most bodies of water have some flow, which tends to 'sort' things by size and weight, so heavy things get dropped where the flow is slowest, usually on the inside of a curve and nearer the banks, and lighter materials will end up where the flow is fastest; out in the centre of the stream or lake, and on the outsides of bends.
So, decide whether you want a fast flowing stream or a slow moving lake (this will mostly depend on your fish), and where the water would be coming in and going out, if your tank was a section of it.
Then you can clump your stuff together in a natural way