Suppose you write in first person. That means you say, "I walked down the path." Third person means you say, "She walked down the path." Let's forget about verb tense for now. If you want to write in present tense, then go for it. However, you're not as likely to have me as a reader.
Second person is possible, but incredibly awkward. Speaking to the reader is sort of like breaking into their apartment and acting like a serial killer. "You are walking down the path." The poor reader might think, "No, I'm not! Wait! Am I supposed to be walking someplace? But I'm sitting here reading. I don't want to walk elsewhere. It's hard to read when I'm walking!"
So, let's just say that second person is out of the picture. I really couldn't advise you on how to do this with any grace or style. If you insist upon second person, then I commend you, but don't expect to sell a lot of books.
Okay, 1st person and 3rd person are both fine, but what if you want to get into the head of another character, perhaps the villain? Can you do this when writing 1st person? If both your main character and your villain are talking aloud referring to themselves, it might be a tad confusing, but it's doable if you carefully divide scenes and chapters and make it entirely clear who the "I" is in each. Also, you'll need to be watchful of voice. Oh, right. Voice. Did you think everybody talks exactly the same way? Of course, your MC is nice, good, heroic, etc. and your antagonist is mean, awful, and villainous. Here's some first person examples if you decide to present both MC and villain in first person:
"I walked down the path, my heart yearning for any sign of my beloved, but I continue to be ever watchful of signs that Mr. Blackness had passed this way."
"I stood in the shadows, watching the poor, sad sucker meandering down the path without a clue that I've got his beloved stashed in a dungeon guarded by ogres."
These examples, of course, are exaggerated to make the point of voice incredibly important when you're writing with multiple points of view.
Easiest to do is third person. Everybody can have their say with little difficulty for the reader recognizing who's the star of a given scene.
Thing is, 3rd person is the writer's voice, the omnipotent story teller from on high (imagine your god-like presence hovering over the characters in your work).
Still, separation of points of view by scene or chapter is the best, easiest, cleanest way to keep the reader on track. You can change points of view between paragraphs, but expect your reader to have to backtrack to figure out who is out front in the story.
If you think you absolutely need to change POV without a scene or chapter break, then your last resort is a paragraph break and a time or place changing word to allow the reader a moment to switch gears.
Fred walked along the path, hoping to find some clue to Hilda's disappearance. MEANWHILE, Hilda pounded on the bars and screamed, desperately hoping to attract attention.
Here the time/place changing word is MEANWHILE. It signals the reader that the story is jumping elsewhere.
Stick to 3rd person. Change POVs only on a scene or chapter break. Keep the voice consistent to the character.
See? That's not so hard, is it?
EXCERPT EXAMPLE FROM SCOTCH BROOM
“Not at all, Barry. Pleased to meet you. I’m Ru...Ron Galdor.” Rune extended his own hand to shake and winced at the dart champion’s hard grip. When Barry turned his back on him, Rune mumbled a quick spell to change the name on his passport from Rune Fenwick to Ron Galdor.
“We’ll play ane-on-ane. Be that guid for you?” Barry asked, twirling one of his darts between his fingers.
“Sure, but I don’t have my darts with me. Can I borrow a set?” One of the men held out his set of three darts. Rune weighed them in his hand. He held up one and sighted it toward the board. “Hey, thanks. These are nice.”
“Da game is 301, double-in, double-oot?”
“Great. Anything is fine.” Rune watched the dart loaner erase the blackboard next to the dartboard and write Barry and Ron at the top. He added the number 301 under each name.
Rune smiled. He ought to make enough for the train in no time at all.
* * * *
“Hello, Ole? Is that you?” Thordis shouted over the Satphone. The sunspots were out and playing havoc with reception.
“Yes, yes. Thordis, so glad you called.”
“We just wanted to check whether Rune had any problem getting a ride to Transylvania.”
“Transylvania? According to Endy, he took the troller coaster to the Shetland Islands.”
“He did, eh? Well, that’s not what he was supposed to do.”
X X X
See, scene changed, POV changed and not even a hiccup in the readers forward momentum. The first scene shows what Rune is actually doing, while the second scene shows his Aunt Thordis discovering that Rune isn't doing what he was supposed to do.
SCOTCH BROOM: Book 3 of The Witches of Galdorheim
A magical trip to Stonehenge lands a witch in the Otherworld where an ancient goddess is up to no good.
While dodging the goddess’ minions and trying to find her way out of the Otherworld, Kat soon learns she shouldn’t underestimate the old has-been for one second; the crone still has a few tricks that can drain a witch’s magic in a flash. To make matters worse, Kat's brother secretly followed her into the Otherworld. Now he’s in danger too. Kat has to go one on one with the goddess to save herself and her brother.