Basic Tips To Write Better Geniuses, Scientists, & Intellectuals
Know what science actually is
This is probably the most important step. Science is a method of discovery, not a philosphy or belief system. It does not nor has it ever claimed to have all the answers. If you actually know what science is and how it works, the concept of "harmonzing science and magic" sounds about as exciting and revolutionary as harmonizing spiral binders and poetry. The simple fact of the matter is that if magic existed as depicted in most fantasy stories, there would be a branch of science dedicated to figuring out just how and why it worked. Scientists would not deny its existance simply because they had no explanation for it yet - they would spend years, even lifetimes working on figuring it out.
An actual scientist would not see something magical and think, "That's impossible because the laws of science say so!" Xe would be thinking, "Well, that looks like magic, but everything we always thought was magic turned out not to be, so this probably isn't magic, either. What's really going on here?"
To get a basic idea of what the scientific method is and what it entails, go here.
Know how logic actually works
When the average person imagines a "logical" character, they often imagine someone like Spock, who does completely ridiculous and irrational things in the name of logic - IE, fail to take important factors such as other peoples' emotional states into account when making decisions. "Logic" in and of itself does not state half the things people say it does. For example, logic does not "dictate" that fairies don't exist. However, it does dictate that just because many people believe in fairies doesn't make them any more likely to be real, because we know large numbers of people believe things that aren't real or true all the time.
To get a better grasp on what this logic thing is all about, I recommend you head over here.
Don't have them know everything about everything.
You know, the Reed Richardsian scientist who can engineer an aeroplane at breakfast, sequence a genome at lunch, and examine ice cores at dinner? Don't do that. Just about every scientific endeavour takes an incredibly long time to learn, and there just aren't enough hours in the day to get to know them all in depth. Add to that the simple fact that most branches of science just may not be all that interesting to xir - a marine biologist just might not care all that much about astrophysics or the chemistry behind making a perfect beer.
Make your character get things wrong before xe finds the solution.
In an early episode of CSI, a character looked at Gil Grissom - a genius by any definition - and made a jab about him being wrong about something. Grissom looked at the character and calmly responded, "I'm often wrong. It's how I get to right." Even the smartest and most educated of people have to go through a lot of trial-and-error when it comes to solving tricky problems, often in part because they don't initially have all of the facts.
Don't make (all of) them dry and dull.
Smart people and scientists come in every personality type there is. Sure, there are those who couldn't crack a joke if their lives depended on it, but on the other hand there are people like Neil Degrasse Tyson who can make death by black hole absolutely hilarious, or the playful Adam Savage best known for his role on Mythbusters.
Don't use big or obscure words where they don't belong.
If you're combing the thesaurus for no other reason than you think a character needs big words to use, you're doing it wrong. Generally, intelligent and educated folks choose large words over smaller words when they are more precise and descriptive than the latter. If you're going to use a large word, ask yourself whether it actually helps to clarify what the person is saying, or whether it just muddles it. Also, if your character is ready to volley an insult, don't flip through the medical dictionary to find the Latin word for 'butt' - just use 'ass.'
Remember that scientists and intellectuals do appreciate the beauty of the world and the universe
A popular misconception is that these type of folks fail to see the wonder in a flower or a rainbow. The truth is, they do - and they're so impressed and captivated by what they see that they want to learn more about it. Learning what makes rainbows shine and flowers blossom only adds to their appreciation. Not investigating or researching them makes about as much sense as putting birthday or Christmas presents up on a shelf forever just to go on wondering what's in them.
Remember that real scientists and intellectuals often enjoy entertainment with bad science
When it comes to science fiction that plays it fast and loose with science, Doctor Who probably takes the cake. But guess who fanboys about Doctor Who on his blog? NASA astronomer Phil Plait, that's who. The man even built a snow dalek in the winter of '09. Neil Degrasse Tyson stated that if the director doesn't care whether the movie is scientifically accurate, then he doesn't care. He also described the movie Armageddon as fun, even though the asteroids did have really good aim.
Remember that they enjoy the same things as everyone else.
Michio Kaku enjoys ice-skating. Phil Plait posts pictures of his cat. While most of them will enjoy doing things that challenge the noodle a bit more than average, many of their interests and likes won't be much different from anyone else's.
Remember, the name of the game is curiosity.
The type of people who become scientists and intellectuals are highly curious folks. They poke, prod, explore, and ask questions (and hopefully, have the social skills to know when doing so would be inappropriate). Because their ever-hungry brains are almost always looking for something to graze on, they tend to observe and analyze what's going on around them. This doesn't mean making observations on the level of Sherlock Holmes, but they will tend to notice more things than the average person, particularly if these things relate to their interests somehow.