First, terribly sorry for my English, but the question is very important, and I'm trying to focus on topic and content.
Sorry, but all of this is started from the end of process not from the beginning.
The basic question is: Are players able to play as the member of the alien race or not?
All these tips are good, but only for alien beings as NPCs. As a constructor (game master or game developer), who want to create some new alien race, you should see this race as a player. The player has a different point of view for an NPC-only alien race than they do for a playable race. Regarding the previous post, let's try to think about this example:
One of your players plays as a alien creature, who is blind and has very strong senses of smell and touch, but the rest of the team play as humans. In this case. the Game Master shall split the team and provide one description of the surrounding area for human PCs and a second, different kind of description designated only for the one alien PC. It is possible, but it's very demanding and only a very skillful game master is able to do this without losing immersion.
The second: each player is human, so he/she thinks like a human. For example: a player who plays as a bird is used to thinking about how to climb a wall, not how to fly over the wall. Or how the player will play as a alien creature which has no hands - for example, how will the PC open a door, when he/she plays as a snake? Will he/she try to bite the door-knob, or wrap his/her body over the door-knob?
I know this example is a bit silly, but it's good to illustrate the issue.
So, the fact of the matter is: how can you create a alien race, which is able to play as a character, not only as NPC? and how will the Game Master shall cope with the differences in game? In this case, the conclusion is simple. Each alien race playable as a PC must be more or less human-like, by which I mean this alien race must have two hands (or equivalent tentacles or something similar), two legs, and at least one head (not exactly literally, but playing as two creatures with one mind controlled by one player shall be very difficult for a player and for a game master).
For example: player plays as two twin fairy-like aliens, who have two bodies but one mind (and cannot be separated for a distance longer than 10 meters). So if one of the fairy's bodies sees or hears something, the second sees or hears this too. But the bodies can act independently. How will the game master deal with the player who is able to be and act in two places at a same time?
A more complicated example is a player who plays as a swarm with one mind. This kind of swarm is able to send its members as a scouts and trespass through small holes in walls, and is able to disperse itself in order to hide.
Consequently all the issues mentioned above will strongly affect the game, gameplay, and probably the game's scenario. The main game master's (or game developer's) responsibility is to make sure the game and gameplay is consistent and playable.
So the best advice is: each game master (or game developer) must not create an alien race that the game master and fellow players cannot cope with. So at the start, the game master should honestly evaluate his/her game and storytelling skills, and evaluate the players' skills.
That is why many alien races in games are human-like. For example: D&D series and Mass Effect. All those elves, dwarves, orcs, etc. are human-like because of fact that those races must be playable for beginners and intermediate game masters and players without ruining the game and gameplay.
So when the game master wants to impress, shock or amaze the players, it is quite simple to create an alien race. But each game master should know that sooner or later, players will be curious how would it be to play as a this alien race - and this is a far more complicated story, because a good game master always must think three steps ahead.