ECCENTRIC training is lowering a weight under control over an extended time (I usually aim for 6 seconds). This is one of the most effective ways of increasing strength, muscle growth and preventing injury. So rather than increasing the weight consistently you can reduce the weight and increase your time under tension in your strongest phase (eccentric) and find a different avenue to pursue if you reach a plateau.
ISOMETRIC HOLDS are when you hold a static position in which there is no visible movement in the angle of the joint. This is another variation to use to build strength but in more specific parts of movements which you may struggle in i.e. the bottom of a bench press. You can lower the weight under control and hold the bottom position (3 seconds) and then press. This is a good method for addressing weaknesses in your movements.