It takes some miles to ride in a Brooks saddle. By greasing the saddle from the start, it gets a bit more supple so it takes less time to ride it in. Recommendation: grease the saddle during riding in multiple times, then once every 3-6 months. Do not use other grease, which can contain plasticisers which can make the saddle limp and increases wear.
Note: the saddle of course is greasy after use, so can leave stains on your clothes. Leave on and wipe the saddle after an hour with a dry cloth.