Written some 60 years ago, Information Theory and Coding by Abramson[1] is an absolute gem for those looking to get into info theory. The cover book [2] being the more complete resource (and somewhat of a grad level defacto standard text).

[1] https://www.amazon.com/Information-Theory-Coding-Norman-Abra...

[2] https://www.amazon.com/Elements-Information-Theory-Telecommu...