#sujood

Sheikh Uthaymīn رحمه الله stated: "This is because he has placed his forehead (face) - the highest and most honourable part of his body - down into the ground where people treat upon with their feet, in doing so he demonstrates the perfection of subservience to Allāh."

The one standing up is actually higher up physically than the one down in prostration, however since the prostrating one humbled himself to Allāh, consequently Allāh raised him and so he is actually closer to Allāh."

So if is appropriate you make plentiful supplication in these prostrations - whether obligatory or supererogatory prayers -, and you supplicate for whatever you wish (after completing the prescribed supplications) as long as it's not a sin or cutting the ties of kinship.

So a student of knowledge may ask, "O' Allāh increase me in knowledge and grant me understanding and memorisation", the one building a house may ask, "O' Allāh aid me in the completion of the house", the youth may ask "O' Allāh grant me a wife", ... and so on."