Strong's Concordance takes every single word of the KJV or the NASB and lists where each word can be found in Scripture. It helps you identify where that word is used throughout Scripture. You then can use a Greek or Hebrew dictionary that uses the Strong Numbers to find the Greek meaning.
Bible Study Tool's Strong's Concordance
Marking the text is a wonderful way to slow down, observe the text, and detect patterns that can aid in your interpretation.
How to easily read a passage from different translations using Bible Study Tools.
NET Bible - This is one of my favorites because it includes notes that help you see why the translators used certain English words for the Hebrew or Greek text. It almost serves as a built-in commentary.
The NET Bible includes translator notes (tn) which help you understand why they chose to use a particular word in a passage. Their study notes (sn) provide some commentary on the passage. It also has an easy passage parallel tool for you to compare passages from different translations.
Using cross-references can be helpful to learn how other authors have handled a specific topic or word. It can also help learn the context of the passage and how important a topic is by how many times it was referred to.
Bible Hub's Bible Atlas
Bible Land Maps - Broken down by biblical periods.
Rose Publishing Maps (via Blue Letter Bible). This has four good maps of Paul's journeys, Ancient Middle East, Book of Joshua, and New Testament Holy Lands
Bible Atlas from the Access Foundation (pdf with some beautiful maps)