Don't be out to "get" the characters. The point of a good adventure is to have fun and if the players feel that the gamemaster's sole purpose in life is to kill them, they won't have much fun at all.
Go easy on them. Make the gaming sessions challenging, but don't be afraid to throw in a few cake-walks once in a while. You can put characters in situations where they have a fairly low chance of getting injured/killed but still make it exciting. Consider a situation where player characters who have average skills of 8D are in the middle of a blaster battle with Stormtroopers who have average skills of 3D. Instead of saying:
"The Stormtroopers are firing at you, but they aren't even coming close."
Try something like this:
"Blaster bolts are flying all around you. Whoa! You feel the heat of a blaster bolt sizzle past your ear. It crashes into the wall next to you and showers you in sparks."
This gives the action a sense of urgency, giving the players the impression that they are in grave danger. In reality, it's unlikely the Stormtroopers will harm them, but they don't need to know that. Maybe these aren't normal Stormtroopers, this could be a unit of Imperial Royal Guards assigned to a Stormtrooper unit. There are other ways of making an adventure seem challenging and dangerous than simply throwing a large number of highly skilled adversaries at the players.
Be as descriptive as possible. You have to be careful not to give too much description that it bogs down the adventure and becomes tedious, but more description is usually better. Details bring your settings and NPCs alive, helping the players better visualize their surroundings.
Draw pictures. Drawing a quick sketch of the layout of a building or a city street is very helpful. This is especially helpful when a battle is about to ensue. It's helpful for the players to be able to see the environment their character is in. They can look at the picture and see where their characters need to be in order to get the angle on those Stormtroopers hiding behind that speeder, etc. The pictures don't need to be overly detailed, just a rough sketch will do fine.
Introductions, please. If the player characters don't know each other, facilitate them meeting quickly if they are to work together during the adventure. Don't wait for the characters to introduce themselves to each other, do it for them. Many good adventures have been ruined because it took the characters two hours to meet each other and get organized. If the adventure involves someone hiring the characters for a job, hire them all separately and tell them they'll be working together. Don't be afraid of even starting an adventure in the middle of the action.
"You were all hired by a man named Acear Vikos to protect a shipment of weapons. The weapons are being shipped to a group of Rebels on Rasyn IV. When you arrived at the spaceport, the weapons were already loaded in a battered Ghtroc 720 freighter that had obviously seen it's share of action. The pilot of the ship, a rough-looking human named Juit Caramon, hurried you aboard. His astromech droid, R6-D4, beeped loudly at you as he hurried to prep the ship for takeoff. During the trip through hyperspace, Juit informed you that you are to deliver the weapons to a Bothan named K'tala Jost, the leader of the Rebel cell on Rasyn IV. You are just coming out of hyperspace and can see Rasyn IV in the distance."
This way, the characters are all in one place with the same objective. They know what they are supposed to do, who hired them, who they need to contact, etc. after only a few minutes of playing time. You have to be careful using this approach, as players may not enjoy being put into a situation with no input. If you're going to use this method, you need to explain to the players why you are doing it, that it will help the adventure get moving quicker. This can also be helpful if you have a limited amount of time for your gaming session.
Develop adventure ideas from real-life situations. You don't necessarily need to think of adventure ideas on your own. Use situations from the news, movies you see, books you read, etc. A recent adventure I played was inspired by the movie Blackhawk Down. The idea was easy to come up with as we had just seen the movie, and it was one of the funnest adventures we've had in a long time.
Give me a break! If the players are playing well, being creative, working together and having fun, give them a break if the dice rolls don't go their way. If this situation presents itself and you think that the players really deserve a break because of their creativity and quick thinking, bend the rules. If a stormtrooper happens to roll extremely high and would otherwise defeat the characters, come up with a creative way of turning this around for the players.
"Just as the Stormtrooper takes aim, a stray blaster bolt ricochets off of the wall next to him and sends a shower of sparks into the face-plate of his helmet, sending him back behind the corner to take cover."
"Just as the Stormtrooper takes aim, a speeder with a terrified-looking Sullustan at the controls careens across the street, temporarily blocking you from his view."
You are the gamemaster and have the right to bend the rules as you see fit, as long as it fits in well with the situation at the time. The players will never know the difference, and will probably have more fun because you did it.
You asked for it! If the players are being extremely stubborn or just plain stupid, feel free to let them suffer whatever consequences they might face. Give them a few warnings and hints, but if they continually ignore them, it's their own fault.
"What? You want to spit in the face of that Wookiee sitting at the bar? Roll the dice for your Alien Species skill before you do that. Ok, you seem to remember that Wookiees have been known to rip peoples' arms out of their sockets when someone spits in their face. You still want to do it? Okay..."