There are many reason of cracks in the building, main reasons are due to drying and shirankage, chemecal reaction and foundation movement and foundation settlement etc.
In your building Iam in opinion that there is case of foundation settlement and I think you have not made plinth protection. Some water percolate through siol in foundation and there by settlement in the foundation.As per your ceiling cracks in slab, which might be due to settlement, by using fine material in RCC, or sand with execive silt is used.
Construction plinth protection if not made, Ensure that there is no any leakage in the sewer or water pipe line or frome open drain. Repair the cracks as given in the artices of HOW TO REPAIR CRACKS. LINK GIVEN BELOW
The drying and shrinkage effect can be minimise to use required quantity of cement. Some time mason add extra cement for the reson to enhance the strength but after some limit it will not benifit the structure and excessive cement gives greater drying and shrinkage. If you use more fine material than there is more drying and shirankage.Some time mason add more water in the mix for easy and to save time and labor is one of the main cause of cracking specially in floor. Improper curing is also one of the cause.
Curing for wall masonary should be done at least for 7 days. For Rcc Roof the theoritical curing is for28 days but practically do curing at least for10 days i.e. water should stands on the slab like POND.
At least 7 days shuttering should be kept under horizontal surface in case of slab.
In plinth protection, construct support wall/ toe wall. Than compact the earth with rammer and lay lean cement conc and compact again. Then lay floor with c.conc. 1;2;4 or any other floor finishing as per your choice.Care hould be taken that there is proper slope from building to out side.