I'll recommend three drawing books which are great for beginners, and they can be found at NLB libraries.
In order of preference,
Keys to Drawing by Bert Dodson
The instructions are straightforward. Lessons are short and fun. Content is accessible and thorough. You'll improve instantly – no kidding.
Even after you have gone through the book, it's still a really nice book to flip through for ideas and inspiration.
Among the books mentioned here, if you can only buy one, buy Keys to Drawing
The Drawing Breakthrough Book by John Hastings
The teaching method is roughly similar to Keys to Drawing, just that it's taught by a different author with different examples.
There are lots of step-by-step tutorials to follow through.
Expect to improve instantly with this book as well.
The New Drawing on the Right Side of the Brain by Betty Edwards
Again, the drawing fundamentals taught is Betty Edward's book is similar as the other books mentioned, just that this book is more text heavy. But it also has many hands-on exercises.
Different people learn things differently. Some prefer hands-on, some like books, some like to observe other masters by standing beside them.
By the way, the improving-by-standing-beside-masters-looking-at-how-they-draw method actually works. I know of people who know nothing about drawing, after standing beside the masters for a few months, suddenly they can draw very well. On hindsight, they must have learned on their own time back at home.
Personally, I think it's faster to learn from books than getting a one or two tips here and there on Facebook. Those tips are useful for improving specific areas. To improve all around, and get the bigger picture, definitely grab a book — it's faster.
If you want constructive suggestions on how to improve your work, just post your work on the USK Singapore Facebook pool and ask for suggestions. If you don't ask for suggestions, most people will just click Like only and not say anything, well, because they don't know that you want them to say something.