Here is my suggestion: Work a lot on your first session. Make the location where the PCs first meet an interesting town with interesting NPCs that they can interact with.
Also don't introduce the PCs to each other all at one. Let them meet in small groups, and make it in a way that they can't be sure of these people's agenda at first. "It seems that a shift-looking person has gotten the same room in the inn as you did. What do you do?" (Note: In medieval times, it was pretty common for strangers to share a room...)
Here's an example from our
GURPS Warhammer campaign:
First, I put some thought into the starting location. I created a town called "Bad Tiefenbrunn", a very small city famous for its hot springs. It was a peaceful and quiet town... too quiet.

One of the players told me that he wanted to play a halfling innkeeper and militia member, and who has I to reject such a great hook?
Other prospective party members included:
- A thief.
- A gambler and soldier-of-fortune.
- A soldier
- A dwarven Trollslayer who wasn't too bright (for those of you who are unfamiliar with Warhammer, Trollslayers are dwarves with a serious death wish - and that's
not a metaphor...)
So the adventure started when the halfling's milita patrol stumbled across a weird-looking dwarf with a head wound who was dazed and wandered aimlessly around the forest. The militia patrol decided to put him up in the halfling's inn because he was the one with the most room (ain't democracy great?). The dwarf's wounds healed over the next few days.
Next, a caravan came into town. A small girl distributed flowers to all members of the caravan and said "Welcome to Bad Tiefenbrunn!" - and was promptly scolded by its mother for giving flowers to "mere guards" (throwing in a few NPC encounters like this adds a lot of color to a town) - two of the guards were, naturally, two PCs who had been hired previously to guard it. So the gambler and the soldier-of-fortune had entered the scene.
One other character who had travelled with the caravan - the thief - made his way to the vice mayor's office (At this point, I took the thief's player out of the room to explain all this in detail). The vice mayor, a certain Martin Hofhammer, had previously hired the thief to "recover" a family heirloom, and asked him if he was interested in another job. The thief said "yes", and Hofhammer explained that his town had experienced some "bandit trouble" as of late, and he needed someone who could get "into the bandits' mindset"... They worked out the details (such as the fee), and Hofhammer asked the next two people to come to him - the two previously mentioned caravan guards.
He explained to them the problem with the bandits, and asked them if they were interested in helping dealing with it. They said yes, and Hofhammer introduced them to the first PC - without mentioning the "thief" bit. Then he told them that for "political" reasons, he would have to put a local in charge of the investigation - but he had already someone in mind, and that particular halfling shouldn't present any problems if they were firm and looked as if they knew what they are doing.
Then I (as Hofhammer) called the halfling's player out of the room. First, I told him that Hofhammer let him wait half an hour in front of his office, with a large cuckoo clock as his only companion. Then Hofhammer called him in, greeted him cheerfully, and asked him whether these malicous rumors of food poisonings at his inn were true. The halfling immediately grew flustered and naturally denied everything.
With the halfling off-balance - and thus in the right frame of mind - Hofhammer told him that a halfling member of the City Council had recently complained to him that "there were not enough halflings in a position of authority in this city". So he, Hofhammer, decided to rectify that, and put the halfling PC "in charge of dealing with the bandit problem". Then he introduced him to the other PCs, gave him 100 gold crowns for additional expenses ("but I want to see reciepts for everything!") and the right to draft others into this as long as they were volunteering, and shoved him out of the door.
And after a few futile attempts to draft other members of the halfling militia ("My wife will beat me if I stay away from home for that long!"), he decided to draft the dwarf...
So now the party was together, and they could start plotting on how to find the bandits...
If you start the campaign on the right note - by introducting each party member like this - your players are much more likely to role-play than by just throwing combat encounters at them from the beginning. And that's worth more than any rules changes or XP penalites...