"Born To The Banner"
This is more or less a continuation of the Tutorial. If you completed that you will have no problems here. The recommended course is to head to the River Fort, which is just out of range. Before leaving, however, note that you can recruit here. You can only recruit Peasants for now, and will be able to get better units soon. In general you should save your money for the Archers and Spearmen to come, but it might be nice to bring in a single Peasant now for a special mission. After that, everybody should head towards a village. You might as well park Deoran at 16, 8 and move the Spearman towards 24, 8. Turn 2 you reach the River Fort and are rewarded by an Infantry Lieutenant joining your forces. Sir Gerrick will be able to supply your troops with weapons and armor to make Archers and Spearmen. Now you can send Deoran back to the keep to recruit in earnest. If you recruited the Peasant last turn, send him towards the 'village' in the river at 6, 10. This might be considered a little bit of spoiler, but you will find something good there. Actually, if you make a concerted effort to flag all villages [You ARE, aren't you?] you will eventually find this, but you might not be aware that this is a village. Besides, if you get there too late it won't help this scenario...
On turn three Deoran should be back in the keep recruiting Bowmen. Bring in the occasional Spearman, but the bulk of your forces now should be Bowmen. This is because the Urza mostly recruits Thugs, which have no ranged attack. Once you've discovered your enemy's weakness, you're halfway to defeating them. Even with your Spearmen, you'll want to stick to thrown spears at night against the Thugs unless your target is wounded enough that you are likely to finish it off. Your other forces are too skimpy to accomplish anything now, so have them continue to capture unallied villages. One keep worth of troops [four units] is likely not enough to last all the way to the Urza, so go ahead and stay for another round of recruiting. By turn 5 you will be nearly out of money, but will have a decent size force along the Northern bank of the river. It's okeh to run out of money this early in a scenario, as you'll be earning more income from your villages every turn. This in now night-time, during which your [Lawful] forces will be weaker and the Bandits [Chaotic] will be stronger. Short of suicide, the reasonable thing to do is to assume a defensive stance until the sun rises.
By now your troops will be somewhat scattered. You might want to get used to tapping the "n" key several times before ending your turn. "n" brings the focus to next unit that has any movement points left. This way it will be easy to find those units you might have forgotten. Most of your units should be arranged in a line [more of a crescent, really] from the River Fort going East. Moreth [the original Spearman] might have gotten all the way to the village at 22, 12. If so, he could be safe there, unless you see several enemy units moving his way. Another gamble would be moving the Peasant down to 5, 16 and send the Mermen, if any, into the middle of the swamp. This could be enough of a distraction to split up the Bandit army marching towards the river fort. These are the only of your troops that will be somewhat safe South of the river.
Normal advice is to put leaders and healers in the 'second line' behind the front line. You don't have any healers yet, but Sir Gerrick can help lead. Depending upon what difficulty level you selected upon starting the campaign, Deoran is probably only first level. Note that leadership only applies to units that are lower in level than the leader. A first level leader can only lead Peasants and other zero level troops. Sir Gerrick will be able to direct the fire of your bowmen to better effect and will also be able to exert his influence on Deoran. It will be a priority for you to get Deoran enough experience to advance to the next level without getting him killed. Ideally you'd also like to minimize the number of times he becomes wounded bad enough to have to pull away from the battle and retreat to a village for healing. Usually this is accomplished by having your other troops soften up a target such that your leader can get the kill. You don't have to attack every character every turn, particularly if it looks like you'll take more damage than you'll dish out.
On turn 7 the daylight comes: your counterattacks will have more effect, and you should be crossing the river in force on turn 8. When you capture the village at 15,12 you will be rewarded with Aleron, a Peasant who is Loyal to you. In game terms, he will work for you for free [has no upkeep]. Since he is only a level 0, there's no upkeep cost anyway. Big deal, right? Well, it is. You should make every effort to keep those Loyal troops alive, and those should be the ones that reach the highest levels. If Aleron becomes a Halberdier [which normally costs you 3 gold per turn to supply], he will still be Loyal and cost you nothing. The Mermen are loyal as well, so keep them alive. That means don't throw them away on land attacks. Keep them in the river or swamps where they are better adapted. After you have crossed the river, leave them behind as a rear guard.
As you press towards the Urza, the majority of your troops will be funneled along the road South. A few should come along the edge of the hills in order to attack the enemy keep from due North. The idea here is get the enemy to split up his forces, or you'll have an unguarded area to attack. By turn 9 you should be in more defensible terrain [forest, hills or mountains] as night will be falling again. Hopefully you will have dispatched the majority of the baddies in the battle by the river, but a lucky strike by some bandits could still cripple you. By the way [this is a matter of playing style] i usually pull a unit back for healing once its health bar turns yellow or red. There are times when you have to sacrifice a unit to achieve some bigger goal, but you'll never get your units to level up if they get killed before they get enough experience...
By turn 11 or so, you should have captured all the villages on the map. On turn 12 i would expect to see some of your units in the enemy keep. The keep is the best defensive terrain; also, the more of its area you fill up, the fewer fresh troops the enemy can recruit. By turn 13 your troops could be attacking the Urza himself, and daylight is coming. With luck you can finish him off on turn 14. Since the enemy keep is mostly surrounded by forest it gets kind of fussy juggling all your troops around so as to rest the wounded, bring your attackers where they will do the most good [Archers against Thugs and Bandits, Spearmen against Poachers], and get the most from you leaders. If it not obvious, you can have Sir Gerrick direct several attacks, move him, direct more attacks, etc. Optionally he can finish his turn by attacking. Ideally you'd like the killing blow against the Urza to be delivered by Sir Gerrick or [better] Deoran. That way he can accumulate enough experience to eventually advance.