At the beginning of the game, you will only have a few juvenile scavengers and 1 juvenile molerat to practice on. Though those monsters are easy targets and easy experience, make sure you save your game frequently on different save spots.
After talking to Diego, messing around and getting used to the illogical user interface, kill the 2 meatbugs that you will encounter quickly after passing the guards. To do so, fight with your hands and pick up the meat from the dead bugs, you will need them for later. Experience 20/500. Keep going and follow the upper trail that leads you to a suspended bridge. Cross it and pick up the rusty sword (10dmg). Equip it and then kill that juvenile molerat. Experience 60/500. I would recommend that you attack by using the right and left swing with your sword. This is the easiest way to kill monsters at this point, in my opinion. Go back down and kill both of the juvenile scavengers. Experience 140/500. Keep running down the path. From that distance you might be able to see the old camp, which is where we are going to. Follow the trail and you will find two more juvenile scavengers. Experience 220/500. Easy kills aren't they ?
But if you think that Gothic is an easy going game, think again. From now on, any monster can rip you apart in no time. Be warned, Gothic is a tough game due to an awful combat system. But you probably have figured out already, haven't you ? ;) You will get over it soon :)
Anyway, keep following the trail, cross the bridge and talk to the guards at the gate. Keep your loud mouth shut and they will let you pass. Once inside, take the right lower path (by the pond) until you meet Whistler, sitting on a bench. Talk to him, accept the quest and take the 100 ore. Keep going further until you meet Fisk. Fisk is selling the sword for 110 ore, so you need 10 more ore. Go back to Whistler and ask for the 10 ore. Back to Fisk again, buy the sword... and keep it for yourself! A slacker doesn't need a sword anyway. Whistler's sword (20 dmg). Needless to say that Whistler will get pissed off at you and will fight you if you talk to him. No big deal, you just have to avoid him (don't run by him too close) and you don't need him to vouch for you to take the test of faith anyway.
Keep going toward the south gate, right after the ramp that leads you to the south gate, and you will notice a ruined building with a bed inside. Since nobody lives there, you can use the bed to heal your wounds anytime you want. A little bit further down the path, you will see more ruins to the left, and 3 roaming meatbugs. Kill those (with your bare hands) and pick up the meat. Experience 250/500.
Exit the old camp through the south gate, and soon enough you will see hell mushrooms. Harvest them (you need 5 of them). You should be able to see 3 molerats roaming nearby. You need to kill them and loot the amulet from the corpse that you will find in the cavity. Experience 400/500.
Go back to the old camp through the south gate, turn right, pass by the ruins and follow the path until you meet with Snaf. The cook is asking for ingredients for his recipe, which you already have. So give him the mushrooms and the meatbugs to complete the quest. Experience 500/500. You now are a fierce adventurer level 1. Yay!
Now it is time to spend those 10 skill points that you just received. In order to use Whistler's sword, you need more strength. Diego can help you with that. Go to the castle's entrance, talk to Thorus first (otherwise Diego won't teach you anything), then talk to Diego and use up your skill points to get +5 strength. Diego should be behind you by the way. Equip Whistler's sword. Scavengers, and later on wolves, will still be challenging though, but now that you got 1 level and a nice longer sword, things will go much smoother for you.
Don't forget to talk to Sly to complete the quest Vanished guard and give him the amulet that you have found earlier. Whether you decide or not to join the old camp, is up to you.
When you will hit level 2 or 3, go see Bloodwyn, who is patrolling on the upper path between the market place and the north gate. He will offer you protection for 10 ore a day. Accept the deal, this way you can beat up miners without being killed by the guards. Loot their stuff while they are unconscious and steal contents of their chests. Cruel world, but easy money ;)
If you have played mmorpg before, it should be easy for you to split up group of monsters. Single pull as often as possible, hit your foe and if things go bad, run away and your enemy will stop chasing you. Heal up, save and go back to fight. Enemies don't regenerate their life, thanks Piranha bytes for that! I assume that lots of people use that method.
Well, I hope this guide will help you to get started and avoid frustration. Gothic 1 is a worthy game :)