An increased frequency of bulb failure could have a number of causes, or even a combination, but there are some steps you can take. The choice of bulb may contribute to more frequent failures - brighter high performance bulbs do offer more light but can expire more quickly, so you could try longer-life bulbs or OEM standard bulbs. When changing bulbs it would also be worth taking a close look at the connectors and associated wiring, as any corrosion with the metal connections or degraded wiring can cause additional heat and result in the bulb wearing out more quickly. It is also possible that the alternator is putting out too much voltage, but we would expect this to show up with other electrical faults if this were the case.