There are three helpful methods for determining if two triangles are similar: AA, SAS and SSS

AA (Angle-Angle): If triangles have two of the same angles, then the triangles are similar.

SAS (Side-Angle-Side): If triangles have two pairs of proportional sides and equal included angles, then the triangles are similar.

SSS (Side-Side-Side): If three sides of one triangle are proportional to three sides of another triangle, then the triangles are similar