The jury is still out on the best way to study the Bible efficiently. On the one hand each book is complete in itself and deals with specific aspects; on the other hand important threads run through and connect the different books. The Bible is designed to contain a lifetime of study, so we cannot expect to master it in weeks or months.
As you probably realise all of scripture is important.
2 Timothy 3:15 and that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus. 16 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, 17 that the man of God may be complete, thoroughly equipped for every good work.
The New Testament writers continually quote from the Old Testament and if we have a Bible with marginal references we will have many additional connections from book to book.
The word of God is intended to be our daily bread and there is benefit in reading portions of it every day. I can recommend a daily reading plan consisting of 3 readings (2 Old Testament and 1 New Testament) each day which goes through the whole of the OT once and the NT twice each year. This provides a useful and balanced background to additional study that we make.
The Bible is constructed in such a way that different books give additional information on particular subjects and only by bringing them together can we arrive at a complete understanding.
Bible study is greatly facilitated by access to the original Hebrew and Greek via Strong’s Concordance. Computers make searching for the words in the original language much easier. Seeing how the words are used in different places in scripture frees us to some extent from the doctrinal prejudices of the translators. This is particularly beneficial when we live in an age with so many different translations each claiming to be better than those that went before.
Here's a website where a daily reading guide may be viewed and printed.
Daily Reading Plan: (please click on the title)
Here's a companion site where you will find useful comments on the day's readings.
Daily Readings with Comments: (please click on the title)
Here's a website where tools for Bible study may be downloaded for free.
Online Bible: (please click on the title)
I hope this helps.