Keep in mind what you put on top of the lettuce. If you spread hot meat over the lettuce, it could wilt. Consider layering cheese, beans, or rice on top of the lettuce. Fill your taco without overdoing it. Avoid filling the shell too full. Hard shells will usually begin to crack with the first bite. The more filling you have, the messier it will be. Overfilling a soft taco will make it harder to wrap and might cause it to tear and lose its filling.
Be prepared in the event that filling does fall out or your hard shell breaks. Have a fork or chips nearby to scoop