There are two techniques: Substitution method and Elimination Method.
Substitution Method is better to use when the equation is explicit or when a variable (either x or y) is isolated on one side.
We can also use this method even if a variable is not isolated on one side, we can try isolating it. But if isolating it will lead as to fractions on our equation,
we may prefer using Elimination method instead.
Elimination Method is better to use when there are many equations involved. It is my favorite because it do not need to apply Distributive property just basic (Multiplication, addition, division, etc). I always ask my students to use it when solving system of linear equations.