To improve endurance, you need to overcome fatigue. To overcome fatigue you need to be able to adapt e.g. add a new training demand and adapt to this…shock the body into changing!
To develop muscular endurance, you have to work at less than maximum intensity. So if you previously performed compound exercises such as bench presses or lat pull downs…try dropping the weight to say 50-75% of your 1 rep max, hence enabling you to increase the rep range to 12-15, or perform weighted press ups and pull ups e.g. hanging a weight plate from a belt to progressively aid progression!
To help buffer the hydrogen ions and lactic acid that builds up towards the end of a training session, bringing you to a grinding halt, try introducing a Nitric Oxide supplement such as BSN NO-Xplode or MusclePharm Assault.
To maintain direct phosphocreatine energy levels and increase power, try a good quality creatine such as Optimum Health's Ultimate Creatine Monohydrate.