A performance review is not the place to be humble, but a place to tell the truth. A performance review---or professional resume---is one area of your life where you should be absolutely candid about your abilities. Make the most of this rare opportunity.
This is business---not church. Objectively, your employer needs, periodically, to be reminded of your value to the organization. You are an honorable person doing the job to the best of your ability--they're not paying you for nothing--so remind them in a dispassionate and fact-based way. Note the jobs you've finished, the progress toward a goal that you've made, the knowledge you've acquired, the educational opportunities you've taken, the number and names of the customers or clients you've solved problems for, the professional relationships you've created or advanced, the ways in which you have contributed to profitability, lowered loss or otherwise helped to improve the organization and its reputation, the number of clients you've added to the roster, the times when you've assumed leadership, etc. Use dollar amounts, specific names, percentages---facts.
Be your job ever so humble, you can still provide your employer with useful facts. It is valuable for any employer, for example, to be reminded that you always show up on time, or volunteer for odd shifts. It's priceless to you if you can give examples of when you stayed an extra 5 minutes, made a deadline or addressed a problem the boss hadn't yet noticed. These simple qualities, oddly enough, are hard to find in an employee and will put you in a class by yourself. If you are telling the truth, it is not a boast or sinful pride.
Most people are so inculcated with the idea that they shouldn't toot their own horns that they don't even recognize the value of their work and are unable to articulate it when asked to. (Unfortunately, they are more than offset by the few who do a mediocre job, yet possess great self-esteem and own a bullhorn.) Being too humble is just as bad as being too boastful---neither is accurate. I say this as an ex-executive who has had experience hiring and firing.
In preparation for your review, write down a list of every task you've undertaken since your last review, down to the smallest detail. It will remind you of your worth and give you some ideas in preparing your response.