and second

Well to be honest its all kinda handmade - so no much of tutorial :] - in color ones its only paintbrush, pen tool, layer mask and some changes in blending modes of layers like overlay, color etc (but no layer effects like glow, shadow etc - they are usually worthless and look bad ) - not much of some mysterious tricks

And well I guess you should just practice as much as possible - with adding more details to the next works and so on Making photo collages like this (black ones as color one are made just of girl pictures + paintbrush for light efects and vector mask for hiding parts of the body) has just one easy secret - you need to blend elements so the boundary between them is invisible and it seems like one part. You can do it also by adjusting lights - like on the color ones - the red strings of light emit glow - and so u need to add some redish / orange lighning to a body. On the black one with cereal field and machine there is a sun (white area) and for example I added around it a lot of thin white lines to create kinda flare/glow effect - it also counts as blending. Same goes for adding texture - especially on black ones - there is a old paper scan overlayed beneath all other layers to make it look dirty - and also helps with blending.

So as I said not much of mysterious tricks

Yes the more layers the more control over it. But not everything is on seperate layers - for example the red strings are flattened - and duplicated at least 3 times as I was lazy and took it from some other thing I did some time ago

Also - if u do sthing always make it big couse as u shrink it, it will always look better - and small flaws will disappear so - generaly I usually dont work on smaller files than a4@300dpi - /2480 px x 3508 px/ - also u need to remember that if u want to print sth with good quality it needs to be at 300 dpi not like things made for web wich are at 72 dpi