there are two ways... first...check the stability of conjugate base...if its quite stable..then it is a strong acid...
second..check whether the specie is deficient or rich of electrons..if deficient..then it acts as acid(lewis)...
one more...more is the ionisation of H+ ions in aquoues medium...stronger is the acid.
Na pine ka shouk tha na pilane ka shonk tha. Hume to sirf NAZREIN milane ka shonk tha. Par kya karen hum nazre hi unse mila baithe jinhe nazron se PILANE ka shonk tha.