Raise the height of the work bench slightly. This may make it easier for you to manipulate small items while you keep your back upright. Make sure you have adequate overhead lighting and an adjustable task light. Good lighting means that you won't bend closer to see what you're working on.
Be careful about resting your elbows on the bench. This can put cause pressure on the ulnar nerve, which runs along the inside edge of your elbow. Take breaks every 30 to 60 minutes to do some shoulder shrugs and stretching. Set up times to remind yourself to check you posture, such as when you check your watch or complete a routine task.