A structured training and diet plan that you follow consistently is one of the top tips that got me results. Without this you are already unprepared. In the early days I would just go to the gym with a muscle group in mind and make it up as I went, then returning home just to eat whatever was in the fridge.  I soon changed this and my physique soon changed too. 

Even with a training plan you can still end up slowing progress with a common mistake that I still make. How many times have you repeated a workout you have done before and picked up the same weight you always lift?  This is a good example of training the same and if you do this you can expect to stay the same. Put your body under new stresses and you will gain new results.Always look to progress with weights, reps, sets, tempos and exercises.  

Low motivation will always lead to slow progress. Always go out there and look to make the most of a session in the gym. There is no point making the effort to go to the gym only then to give 50%.Every time you go in the gym you should look to make it count, giving everything you have into every rep.