It is your job to send an application to the sponsors, in which you declare your clubs' sponsorship requirements. If your requirements are too high compared to other applications you will be rejected.
The trick is to send an application with high requirements - however, not so high that you will be rejected.
When you send an sponsorship application you must fill out "base amount", "bonus amount", and "bonus requirement". Base amount is the number of Credits you will receive no matter what (if the sponsorship application is accepted that is). The bonus amount if the amount of Credits you will get as a bonus hvis you reach the goal specified as bonus requirement (for example to end as in the top five in your league). The sponsors will include the probability of you fulfilling your bonus requirement, when assessing your application.
You application can be changed at any time throughout the season.