GO hosts a number of predefined Slim sets, a generic GO slim, and a number of slims tailored to give good annotation coverage for some well studied/annotated model species. The available GO slimming tools also provide an option to upload your own term set. For most applications you usually need to adjust the terms in the slim to represent your results (i.e to reduce the number of terms, or to replace terms in regions of special interest with more specific children). The generic GO slims or organism specific slims are a good starting point to create your own GO slim. When creating a slim you should still ensure that it covers as many annotated genes in your set as possible. To enable interpretation of your results you should also report how many genes are annotated but not in your slim, and how many genes do not slim (i.e map only to the root node and are therefore 'unknown').