I had to learn how to 'date' as an adult when i was 23 after breaking up with my partner who i had been with since i was 16. Luckily i was unemployed thanks to a redundancy and cashed up so i got to get in a lot of practice in a short time because applying for jobs was far less interesting.
There are books on it, there are some which are quite interesting from a basic human interatction point of view and there are some which are stupidly sleezy even suggesting basic hypnotism. I decided i wasn't above reading a book (see above notes about being unemployeed with a fair bit of time) but i tended to avoid some of the IMO dodgy stuff. Anyway the out takes i got which helped me talk to girls but better yet get through a break up, land a new decent job and just start improving my life.
Have fun doing what ever it is your are doing, the easiest way to appear 'interesting' when you are actually doing interesting things. I learnt how to ride a motorbike, went to raves, drove to 3 hours to attend a university ball of my flat mates sister dressed as Marilyn Munroe (by the way i am a straight guy), caught up with heaps of people i hadn't seen in a while.
Be confident, don't ask and um and err you get no where. I wouldn't ring and ask if they would like to go out sometime in the future and do something, i would ring and say hey i am heading out to do x activity at y time they should come. if they didn't want to i would have a fall back of something else i was doing that i already knew about (see the be doing lots of stuff). People will happily follow a person if they are interested, if not they will have somethign they want to do which you can choose to do with them either way you are working out the details not the question of do they want to do something.
Look better ... if you aren't happy with your look you won't be confident, i wanted to get a bit bigger and stronger, so i went to the gym and got fit which i have found great for other reasons. Changed my hair about 4 times and got clothes that fit well (don't fall for the trap of spending a fortune just get stuff that fits).
practice, i had the same first date a few times, knew a great late night coffee/pancake desert place just around the corner from my house, figured out a few solid topics to talk about if they where to quiet. That type of thing. Its like investing, get to a certain level of competency then you have to take a dive in to keep learning.
I learnt a lot about myself after years of being quiet and passive and previously not being brilliant with girls when i was 15 when i was previously single. I am not some guy slapping away women by any means but i can hold my own in a group and tend to pickup positive responses when i am out and about. I have been in a relationship for 18 months with a great girl and i certainly wasn't out looking for a 'relationship' she was a friend of a mates girlfriend who i met at a friday night after work drinks who happened to have always wanted to go out with a guy who had a motorbike
sometimes a bit of luck helps.