easiest way is to do some bandit hunting with a small but elite party. You get more renown based on the difference in party numbers, slightly weighted to offset quality, and how many of your party get killed/wounded during the battle. eg. You+3 companions vs 50 highway bandits will get you around 20 renown (less if any of your party is wounded); you by yourself between 30-40; with 100 troops maybe 1 or 2 renown. You can even pick up ~10 renown for taking on 10 fures by yourself and a fairly easy battle if you have anything more than starting equipment.
Of course to do this successfully you will first need to get yourself some good armour and weapons. If you really want to make money fast my suggestion would be to do some trading. Visit the cities and villages of Lithuania/Volynia and buy fur for <100 denars; sell in Teuton cities, Polish, Hungary, or Germany for >350. Buy Salt and Iron in Polish, or Iron in Denmark, Germany, or Hungary for <100 and sell in Teuton, Lithuanian, Volynian cities for (Salt >250, Iron >300). If you do just a few of these trips you can make a ton of money and afford to buy the best equipment out there. Also learn how to use the NPC inventory (camp->access companion inventory). When you are buying up supplies instead of relying solely on your personal inventory; you can buy goods and then transfer them over to your companion inventory (maxes out at 99 usable slots) instead of going back and forth with a small amount of goods. If you buy the 99 furs for <100 and fill your inventory of say 30 slots, you have 130 furs you paid ~13,000. I then travel city to city hunting any bandits I come across and only sell furs in cities in which I get >400. So in maybe a week or so of travelling I sell for 52,000 (total profit of 39,000 denars). You'll make almost as much going back the other way carrying iron and salt and if you buy a good blunt weapon, say a heavy long hafted mace; you can ransom all the bandits you knock out (most get you 100 denars each).
PS: don't neglect "looting" skill. The higher it is the more you make defeating even small bandit parties (remembering that loot is split up with your party, so the smaller the party the more loot you get yourself). Also higher looting increases the value, type, and quantity of looted weapons/armour from a battle. Doesn't make a big difference fighting lantriculii, but against Pirata you can pick up some really good stuff, 90 helmets, 40 body armour, fairly good swords and if you don't need them, you can sell for good money.