I think of my ego as being one of the bossy voices in my head, telling me what I should/should not do, what I want, always commenting on things and people around me in a selfish, chatty, not particularly helpful way :-)

I don't know that egos particularly need strengthening, they just need paying attention to. If you default to thinking about others opinions first, you have decided to let them make decisions for you and gotten in that habit. Probably you got in a fight with your mother when you were two and guess who won? From then on you were afraid to have an opinion of your own and it was just easier to let the "bigger" seeming people make the decisions for you than try to fight them. Now that you are older, that decision gets in the way.

Unleash your ego a bit (but still keep him on a leash) and ask yourself, as an adult, what you want to do in a particular case. Remind yourself of ways other people deciding for you and going along with them has "ruined your life". Pay attention to what you want and if you "don't know" look at a situation and decide what would be best for you or what you think you would like! Only you can know what is best for you, you are the one who has to live your life.

I say keep your ego on a leash because it can get to where you go too far in the other direction and listen too much to your ego and not enough to other people. We have to get along with other people and there are trade offs for our ego in doing that. I did not get married until I was 39 and I was thinking of not changing my name to my husband's since I had credit in my own name, etc. I mentioned that to my stepmother and she got angry, insisted I should change my name. I thought about what I wanted (ego) and about my relationship with my stepmother and found I did not care as much about whether I changed my name or not, it was mostly just "easier" not to. I thought about my stepmother's age and how much longer she might live and the two of us have a relationship and how that might be damaged by going against her in this instance and weighed that against how much I cared. I changed my name.

Balance is the key and it sounds like you have gotten in the habit of not paying enough attention to your own ego. It's there, it just has to be consulted and allowed to be "itself". Your opinion matters as much if not more than other people's as it is your life you are living, they are not living your life, they are only living their own.