Make sure that your measure your 'sit bones' and ensure they fall within the cantle plate.
Make sure that the saddle width is appropriate for the style of riding you propose (wider saddles for a more upright riding style)
These are covered
here and
here
In 'breaking-in' a tensioned leather saddle you are aiming for it to mold to your sit bones.
The vegetable-tanned leather is soaked in water then pressure molded in the factory to the shape you buy. You are aiming to fine-tune that shape by applying pressure from your sit bones to the leather which subtly reshapes the leather at those higher pressure points.
Where the pressure is equalized, the saddle is then molded to your riding position.
The process is aided by the normal humidity found at that contact point when riding.
The thicker the leather, the longer the process is likely to take, but the longer the saddle will last. There has been a suggestion that a damp (not wet) cloth on the saddle top for about 30 min then a short 30 min ride can speed up the process of the pressure point equalization. Then let the saddle leather dry thoroughly.
If you apply conditioners to the leather to make it soft and pliable the leather will not retain the molded shape and it will quickly stretch and become unusable. Follow Brooks advice!