One of the best ways to improve is to look at classic games from the past. The main reason these tend to be more instructive than most modern games is that tournaments had a greater range of playing strengths so that players could actually realise their ideas. Modern super-GMs tend to see everything coming and stop it in advance, so it’s very rare that you’ll get a single strategic idea realised.
Isn’t there a problem that the openings are ‘old-fashioned’? Well not really because Capablanca and Alekhine understood very well how to play the openings that were fashionable at the time, in fact their knowledge and understanding of these openings probably exceeds that of many modern players. Are these old-fashioned openings worse? For the purpose of beating an evenly matched opponent they might be excessively simple, but for players at club level this really doesn’t matter. And old-fashioned openings illustrate many important strategic themes with great clarity.
There is of course an urge for players to emulate the top players, whether this be Magnus Carlsen, Viswanathan Anand or Vladimir Kramnik. But in this case my advice is simply to get over it, it takes an immense amount of talent and work to play in the style of these giants and this is well beyond the capabilities of all but a highly select few. And note that even the greatest players played relatively simple openings early in their careers.
So do I have any specific book recommendations? Indeed I do, but it’s neither a recent book or a best seller. Take a look at Imre Konig’s Chess from Morphy to Botvinnik which contains the most brilliant exposition of certain opening systems with explanations about how they developed. Plus it’s well worth studying Alekhine’s collections of best games and Kmoch’s collection of Rubinstein’s games. One thing you’ll need though is to understand English Descriptive notation, the old P-K4 stuff. A lot of the best books were written using that.