Some pretty silly advice in the OP imo. Drop the 'nice guy' act? If you need to do that, you're not only more likely to be more of a wanker, but actually LESS confident and LESS of a catch compared to someone who's confident, successful (with life and with women) and still retains the nice guy tact.
It's easy to be a douche and score pussy, since a lack of morality and conscience, added selfishness, a lack of accountability etc, makes it easy to get what you want and not really care for damage control or the potential repercussions there after.
Add to that, the less of a nice guy you are, the less decent girls you will tend to pick up. If you just want a shag, you might be cool with that, but if you want a decent girl for something long term just remember, decency attracts decency.
Sure, some 'decent' girls go through phases of wanting the 'bad guy', but this is usually an immature early thing that girls with their heads screwed on eventually grow out of. What you'll find is the more mature girls (often more marriageable and decent too) actually do want nice guys.
So my advice?
It's true. Confidence is everything. Forget about potential rejection etc. Just be yourself. Be fun, talkative, attentive, cheeky, sweet, funny, smart, fashionable, all those things and more. But don't force it. If you go in to a situation expecting something in return, often the pressure and expectation can ruin things. Don't look at it like that. You don't NEED the date, NEED the shag etc. just enjoy yourself and the company, and the rest will fall in to place. But do NOT lose the nice guy in you, then you're going down that messy path of basically being just disposable fun and not much more, you will attract more of that yourself too. If that's what you want, fair play, but if you want something decent and long term, don't lose the nice guy in you, just don't be easy or be a walk over. Keep the challenge up, let her do some of the chasing too. Also, never linger or yearn for a girl that isn't showing mutual interest back. It must be a two way street.