How do I win more silver per hit?

Silver per successful hit is always 10% of the REMAINING SILVER the player has per hit (Example, if player A has 600,000 silver and you hit them and are victorious, you will loot 60,000 silver). You can however buy a silver loot buff (this will cost money though) that can increase your loot per hit from 10 to 20%.

When you raid another battlefield during "Deep Battle", the loot percentage is automatically higher than 10% (I think it's 20 or 30%) but the trade-off is that your location is known to the defenders of that battlefield so silver hunting on another battlefield is riskier, but pays more dividends.

The best method to obtaining silver is to send multiple marches out on the same person in quick succession. You get less silver per subsequent hit, but it's the quickest way to drain a player of all their silver. Good Luck!