I you manage to have "long queries" with a 300MB dataset, you're doing something seriously wrong unless your definition of "long" is very different from mine. Or you're running on harware from the 90's.
Run "explain" on all your queries and review your indexes to begin with.
That dataset is so small that there should also be no need to be continuously tweaking the config file. 10 minutes looking at a performance guide, and ensuring you have enough ram to load everything into cache should be enough to get your configuration to a "good enough" shape - there's just nothing reasonable you'll be doing with a 300MB dataset that should need anything but getting the very basics of the config right to perform decently.
Run "explain" on all your queries and review your indexes to begin with.
That dataset is so small that there should also be no need to be continuously tweaking the config file. 10 minutes looking at a performance guide, and ensuring you have enough ram to load everything into cache should be enough to get your configuration to a "good enough" shape - there's just nothing reasonable you'll be doing with a 300MB dataset that should need anything but getting the very basics of the config right to perform decently.