Schedule cron job every day

Question

how start cronjob every day?

I'm not too strong in schedule

<crontab>
        <jobs>
            <ebayautopurchase_deleteproducts>
                <schedule><cron_expr> * * * *</cron_expr></schedule>
                <run><model>ebayautopurchase/observer::deleteEbayProducts</model></run>
            </ebayautopurchase_deleteproducts>
        </jobs>
    </crontab>

Answer 1

<crontab>
    <jobs>
        <ebayautopurchase_deleteproducts>
            <schedule><cron_expr> 0 */12 * * *</cron_expr></schedule>
            <run><model>ebayautopurchase/observer::deleteEbayProducts</model></run>
        </ebayautopurchase_deleteproducts>
    </jobs>