Electronegativity: more electronegative element leads to deshielding of protons and signal appears at downfield and vice versa.
Anisotropy effect: those compounds which are having a double or triple bond involve pi-electron which produces an induced field that may change the position of electrons and hence lead to shielding or deshielding.
Hydrogen bonding: it increases the chain length which results in the deshielding of protons and shifted downfield in the spectrum. If it decreases the shielding of protons and upfield shifting will be there.
Vander Waal deshielding: In the complex molecules, it may be possible that some protons may cause steric hindrance which may lead to the deshielding of protons.