The glass will always take up the mould texture if it touches. So start with smoothing the mould itself. You can do this by wrapping very fine wet and dry sandpaper round a flexible sanding block. You can use this wet or dry, although wet is more healthy. When you get the desired surface texture you can let the mould dry or immeidately apply kiln wash. When this is dry you can again sand the kiln wash but with dry paper only this time and very lightly. Alternatively you can ball up nylon stockings to provide a soft abrasive action. If you sand through to the mould surface, simply apply the kiln wash again.
You can minimise mould marks by slumping at the lowest temperature which can achieve the slump you want.
If you want to avoid mould marks altogether, do an aperture drop and cut off the rim. There is no mould contact with this technique, so the glass retains the surface it had in fusing.