Vacuum leak, dirty MAF, clogged fuel filter, weak fuel pump, leaky fuel injectors, bad fuel pump check valve, Anti-theft system (PATS), bad CKP sensor, bad CMP sensor, weak battery, come quickly to mind.
Clean the MAF. Use only a cleaner designed for the purpose.
Look for any vacuum leaks. Today's cars will not work correctly with even the smallest leak.
Does the theft light come on during cranking? If so, STOP and find out why.
Cycle the key off/on/pause several times without cranking. LISTEN for the fuel pump to run each time. If not, STOP and find out why?
Does this improve starting? If so, suspect leaky fuel injectors or bad fuel pump.