For an entry-level job, you can say that your lack of experience is a weakness, but you are prepared to work very hard in learning the job and that you will be able to do it faster than the average employee (because you have done so at other jobs).
If it's not an entry-level position, think about the type of job it is. Then you can say something that relates being "new" to one particular aspect of the specific job. For example, if the job is heavily team-oriented, you could say "I haven't had much experience in working in a team environment, so I may have to adjust to that. But since I am committed to doing an excellent job, I recognize that I will have to work on that aspect and I am confident I will fit in well." That is a weakness, but not something that is going to kill your chances and it also shows you have thought about the specific work environment.
One thing NOT to say: "I have a tendency to push myself too hard" or anything like that. I have heard that one a million times and it always sounds clichéd.