Have a desire to write a book. How can I improve my writing skills and channelize ideas while doing a full-time job in another field?

Start writing short paragraphs. May prove useful. Putting thoughts on paper is an art and also a skill. Once you are comfortable with small paragraphs then move ahead.

Thanks for the A2A. I'm not sure that I can improve on Jackie's answer, but when I teach creative writing, I give my students practice with working on the following: working through writer's block (just write about something every day ... not everything that you write needs to be in service of your main project), having a plot (the five elements of plot are introduction, rising action, climax, falling action, resolution ... the bulk of your project will be rising action; falling action and resolution may amount to very little), finding the sublime in the mundane (everyday objects and activities can have greater meaning), dealing in abstractions and doing so subtly (writing can teach us about great matters), using some or all of the five methods of characterization (writers reveal a character's personality through the character's actions, through a character's speeches and thoughts, through a physical description of the character, through showing what other characters think or say about the character, and through a direct statement revealing the writer's idea of the character), showing, not telling (probably the hardest thing for the novice writer, but the biggest point for me ... only give the details necessary for your reader to put together your meaning; see Hemingway's Iceberg Theory of Writing), listening to how others speak (good writers give their characters voices that are distinct from each other), and using imagery (language the appeals to the five senses). While the data may be dubious, I believe in the 10,000 hour practice rule.  Start writing without worrying about the end product (and start by writing what you know).  It will be a while before your work gets good. Best of luck!

The big topic here may be the arc. Consider it as a puzzle. Writers can be learned from. A lot of stuff is built-in. It takes unlearning some of what they had been told and discovering on their own. A decade makes a big difference. Write each day to keep the motor running. Maintain a history of amounts. First drafts strive for wordcount. Forms have different lengths. There are the narrative elements. Sources can explain about plot types. There are writing means. Notes are easy, as is email. Pads are handy. Folders and tags are thematic. There is publication. Blogs and wikis are easy. Documents are straightforward. Readers are appreciated. Critiques count. Editing is an art. There are services. Endings can be a beginning. Characters have viewpoints. Complexities can involve dualities. There may be a protagonist vs antagonist, or a romantic triangle, for example. Genres are stimulating. Criticism is a skill. Prompts lead to considerations. Music may calm doubts. Typing differs from handwriting or dictation. Emotions are an art. Setting key dates may stimulate creativity. The voice may take a while to develop, like a clear narrator. The presentation may be unreliable for dramatic tension or irony. Case in point, scenes are stylistic. Try playing with details such as: point of view, setting, time, goal, desire, questions, conflict, description, characterization, senses, mannerisms, faces, gestures, activities, impressions, physical, mental, emotional expression, reminders, similes, metaphors, flashback, dialogue, subtext, wardrobe, props, background characters or crowd, mood, subplots, arcs, event, stakes, beats, twist, pacing, transition, sequel, expectations, decision, foreshadow, or theme. There are early enthusiasm stoppers like admonitions to show don't tell or accusations of stereotyping and cliches. Maintain a portfolio. Writing is explanation so that applies to most activities. There is stuff about people, places, the past, or possibilities. Fiction is suspension of disbelief and holding the reader's attention. This is done subtly in a number of ways by most everyone. Figuring out philosophy is fun. Rand had an ideology. It could be fictionalized. There are others to compare it to. Background research can be saved. Nonfiction also has its charms. There is a lot of literature about writing.

First, I love Fountainhead! I can understand your inspiration. Second, I'm an engineer, too! I understand the need to inject some creativity into your analytical life. Here's a suggestion, try some freelance writing. I'm sure you don't need the money. It's not about the money. It's about adding some structure in order to free yourself to simply write. I wrote a blog post about it https://indiewriter.quora.com/How-Minimizing-Choice-Can-Improve-Your-Writing It really worked for me. My best advice is to write every single day, at the same time. Here's a post about that https://indiewriter.quora.com/Writing-Habits Best of luck! Let me know how it goes.

I asked a good writer once how to learn his craft. His answer was "The only way to become a good writer is to write.  I write something every day, even if the only audience is myself.  I dash if a lot of letters, but I try to write some with great care" (this was a long time ago). I think writing is one of the few important skills at which everyone can get better (and nothing would help you more than a good friend who is a skilled reader and can help you improve).