In my experience, students usually struggle with equations that have variables on both sides because they become confused about what to move and what changes when it moves. I teach them to think of the equal sign as a divider. Put all the variables (letters) on one side and all the constants (numbers) on the other.
One of the biggest mistakes students make is forgetting that the sign changes when a term crosses the equal sign.
For example:
+2x becomes -2x
-5 becomes +5
+8 becomes -8
Another common problem is not understanding the difference between a variable and a constant. A variable is simply a letter (such as x), and a constant is simply a number. If there is a positive or negative sign in front of it, the sign is part of the entire term. For example, -4 is one constant, and -2x is one variable term. When you move them to the other side of the equation, move the entire term, not just the number or the letter.
Once students understand these simple rules and practice them consistently, solving equations with variables on both sides becomes much easier and much less intimidating.