Going to pitch in my pennys worth here as a bloke who has been through the realisation that he new nothing about seduction (yep, using that word as it is a nice catch all phrase for the process). Following my divorce I realised I knew nothing about "chatting women up", a practice I found to be a waste of time.
Going straight up to a woman (or man) and asking them out for a drink results in one of two answers. If the bloke is confident and self assured he may say yes, as he does not consider that a threat. However as you seem to be getting "no" a bit perhaps you might want to do things differently.
Perhaps you might want to look at yourself - do you come forward as an attractive, eligible single female or are you in some way projecting an image of a women who is not available?
When I was married I dressed a certain way and acted as such. I had to unlearn such behaviour and modify my body language to ensure that women realised I was single, but most importantly not desperate.
I looked at new clothes, asked for opinions from shop assistants and a personal shopper what really suited me and made clear that I was single and wanted to find a new partner.
I studied body language and learnt to use more open postures and to walk confidently with good posture.
Most importantly I learnt how to smile and look like I was a fun person to be with.
I also learned how to ask a woman out - it was no use just going up to an attractive woman alone and chatting her up (attractive women are rarely on their own any way) but rather to find a group and engage it. Ask for an opinion - with women I found asking about social situations best (a dilemma involving a friends girlfriend, or perhaps about the social protocols involving taking a friends sister to a wedding).
If you wanted to engage blokes, ask about blokey things. In a bar where football is showing wait until half time and (together with a friend) just ask a bunch of guys about the off side rule. Or what is this new camera thing they are bringing in this year.
Or ask about if they think it is safe to go without a spare tyre and use one of those repair kit/compressor combinations.
It may seem to be perpetuating a stereotype about women, but it gives us blokes a chance to act like blokes - and we like that occasionally!
When I asked groups of women (and sometimes mixed groups) for an opinion I was never, ever blanked or ignored. People like to talk and if you sound interesting and interested in their opinions they will feel valued and like you.
It will also give you the chance to get to know them a little bit before suggesting "Hey, you know, you seem like real fun - is there anyway I could stay in touch with you?"