Being systematic is the best way to go about managing your grant opportunities. There are a few tools that can help you successfully find and manage grants. I like Grantwatch, which is a subscription service, but there there are many other services, including free ones, that will give you information on grants, eligibility and average grant amounts. The Foundation Center is a guide that you might be able to access for free at the public library too and there may be others, so that one is worth checking out.
To best manage your grant opportunities, I would suggest:
Creating a calendar of the grant opportunities for the year, including enough detail to make it easy to reference, such as the URL.
Keeping a tracking document of the grants you have applied for, so that you can submit the grant reports on time, or in advance.
Re-applying for the grants you are eligible for.
Remember, the more systematic and organized you become in your search, the better the results!