I don't find the cover to be very appealing or attention-grasping, and I also don't understand how it is related to the story. When I saw the cover, I expected more of a "random" or Humor story, but definitely not a sci-fi/fantasy book.
I understand the title quite well and I think it is a decent fit, but "The Day They Came" really only works with the first few chapters, as it describes the day that the strange beings came to earth. I think the title would fit the story a bit better if it described the story as a whole rather than primarily the first couple of chapters.
Grammatical and spelling errors:
Chapter 1: "Aleksandr..." You spelled the boy's name as Aleksandr here, but you refer to him as Aleksander later in the story. Be sure to proofread and decide on one way of spelling the character's name. It is confusing to the audience when you constantly change his name's spelling.
Chapter 1: "Her had hovered over the accept button." Here is another spelling error. I assume that you intended to write "Her hand hovered..." Additionally, the word "accept" when you refer to the accept button should be in quotation marks, so that your audience is aware that the button is used to accept Aleksander's Facetime request.
Chapter 1: "He faces time with me and looked so frightened!" I believe you intended to write "He Facetimed with me and looked so frightened."
Chapter 2: "...took the breath out of her lungs and causes her to freeze on the spot." Be sure to keep the tense of your story consistent. Here, the word "causes" is in present tense, and the rest of your story is written in past tense.
Something that I think could be improved are your sensory details. What did Saffron look like? what did Aleksander look like? What did Saffron's house look like? What did it smell like? What was the environment like where she lived? What did the strange creatures look like?
By answering these questions, you will make the setting much more lively, and your readers will be able to imagine the story more clearly.
Some areas in the plot don't make much sense, or they seem too dramatic/unrealistic. For example, in Chapter 1, you explained how Saffron cried "over the loss of her best friend." Why exactly did she immediately think that she had lost Aleksander permanently? If I were her, I would likely be very confused and try to contact him another way. I would never simply come to the conclusion that I would never see him again.
I also don't entirely understand Saffron's relationship with Aleksander. Are they friends in person or did they meet online and become friends that way? If so, where online did they meet, how, and why? Without addressing these questions, your audience can't clearly understand Saffron's feelings and their relationship.
I thought it was very strange when Aleksander mentioned that the aliens looked human, yet their skin colors were actually very bright and inhumane. I think it is odd how he described them to be human-like yet they were actually quite different. I would have expected him to mention their unusual skin colors.
I also feel that the pace was much too fast for your readers to keep up with and remain entertained. I thought your first chapter dragged on a bit much, yet still contained far too many details. I feel that the first chapter would be much more entertaining and very suspenseful if you ended where Saffron and Aleksander were disconnected. This would have left your audience wondering what was to come during the rest of the story.
In addition, I thought it was extremely abrupt when the aircraft landed near Saffron's house. I think the story could use more suspense and more build-up, rather than immediately adding in such a large event. I didn't understand how Saffron's mother died, and there were little to no explanations about it. I was shocked to see how Saffron had almost no reaction, and simply just dealt with her mother's death.
I think the first chapter as a whole is much too fast and the audience struggles to keep up with the events that are occurring. I feel that the story would make much more sense if it were more drawn-out and suspenseful.
I also don't entirely understand the introduction in Chapter 2? What lime green gem are you referring to? How is the blue diamond related to the lime green gem? This could all be clarified, as I had no idea what this section was describing.
Something that I do like quite a bit, are the changing viewpoints. I love how the story is told both through the eyes of humans and through the eyes of aliens. However, I still feel as though the story could be enhanced with more descriptions and sensory details.
I found the characters to be slightly unrealistic. One thing that seemed strange was in Chapter 1 when Saffron begged her mother not to make her go to school. Instead of asking her mother and providing a believable reason for not wanting to go to school, she acted like a small child and begged her mother. If I wasn't aware that Saffron was fifteen, I would have thought that she were closer to eight years-old.
Overall, I think the story could use some changes and improvements. I love the plot of the story and where your ideas are headed, but the story could be structured differently in order to make it more suspenseful and attention-grasping.