If I've got a goal to increase my weight and lead a fit and healthy lifestyle, should I go out and book into a gym and weight lifting program straight away
I'd wait a while and instead start straight away imagining your goal coming true after going to your Peaceful Place and using your Emotional Anchor. What will happen is you will "fall in love" with the idea of being fit and healthy and after a couple of weeks (after your Reticular Activating System has found you the best membership deal in town) you'll be practically bursting down the walls to get into the gym and it'll be a joy to be there.
If you go immediately without reprogramming your subconscious mind, it will be conscious mind "will power" that is at work. Exercising will power makes it difficult and boring. If at some stage you stop using your will power, then it is very easy to slip back into old ways – that old habit is still in your subconscious mind.
First change the old habit to the one that you want, and you'll love every minute of your new fit and healthy lifestyle.