Re: How do you prune your tomatoes?
The short answer, it depends. Some varieties just do that. However, with the leaf browning that follows vein paths I would suspect either they dried out and you watered them heavily or you fed them fertilizer and it was too strong. Nothing that time won't fix. Just try to keep the soil evenly moist and err on the weaker side with fertilizing. I'm no expert though so I'm only speaking from my experience. I would clear the lower leaves up to the top of the marigold heads and then a bit more once they grow another foot. There is already soil on the lower leaves. Soil can spread the fungal diseases that can wipe out the whole row.
My foot's in the door, pm me if you need me.