You need to introduce your characters somehow, otherwise there really wouldn’t be much of a story, would there? How you go about doing that is important and can impact upon the reader’s experience of the story as a whole.
First of all, don’t throw 101 characters at the reader straight away. Trying to keep lots of new names and characters straight is not something readers are very good at, and it gets in the way of that all-important immersion. Take your time to introduce characters gradually, wait until they need to come in, and then give them the space to make an impact. If you have a large number of characters all in need of an immediate introduction, then keep it brief.
For example, ‘A thief, a priest, and two merchants were travelling the Diornie road.’ That gives the reader some idea of the type of characters they’ll be dealing with and some hint of the setting they’re in. In that single sentence, you’ve begun to form an image and an idea of the story and characters in your reader’s mind. By keeping it to the basic details you’ve stopped the reader from feeling overwhelmed. They don’t need to know that the thief is called Bob Vander Schmidt, is 56 years old, wanted in 12 different states, and loves nothing more than a nice bit of mutton. Those details can come later.
The other advantage to keeping it brief is that it gives you more information to carefully convey to your readers at a later date; you keep them hanging on and wanting more. You give hints as to what your characters are doing and who they are, but you leave the questions firmly rooted in the reader’s mind. That gives them a reason to keep reading. They have to find out those answers. Reader curiosity is essential. As the author, you should drip feed them the pieces of the puzzle so that the reader can put it all together and form their own conclusions. Giving them everything up front means they have nothing left to wait for, nothing to intrigue them.
You don’t have to introduce everyone with a huge bang and big fireworks display, just make sure they’re distinct from the rest of the cast and stand alone.
Introduce them in a way that fits in with the point of view. For example, if you’re writing in the first person and the protagonist is a seamstress, then she will most likely notice the clothing first. Don’t have a big alpha werewolf noticing the beautiful blue eyes of the new upstart in his territory; instead, have it open with his body language and threat assessment, then move on from there.
In summary, take your time introducing the characters, and don’t do it all in one big lump. Give yourself and the characters the time and space to make an impact so that the reader grasps onto them easier, and keep it within the point of view. Finally, make sure that everything fits in with the established point of view. It will make a difference and the reader will notice.