I think a lot of 'not having anything to say' is about letting go and talking about random shit. I'm not shy at all, never nervous, quite sarcastic/funny and chip in with the odd comment here and there, but even around friends I used to be quiet. I'd let them run the conversation and I'd chip in. I was fine in fairly formal conversations or where we had a clear mutual interest (football, or work or whatever), but if that mutual interest didn't come up early on or after we'd ran out of things to say about it, I would often struggle to run the conversation myself.
If you like, you could say I had 'conversation management' issues rather than any issues with confidence or being interesting or anything else.
Talking about yourself is fine, but don't over do it or people will probably think you're a bit of a bore/boast. Likewise, letting the girl talk about herself is fine, but don't turn it into a question and answer session where you basically just ask her question after question.
As I mentioned earlier, let go and just talk shit. Think about the canned lines. What are they on about? Most of them talk about something completely inconsequential and are often just downright stupid. But many of them work. Why? Because - cliche alert - what you say isn't important really. It's the emotion you're evoking.
Even when people say "it's not what you say, it's the way you say it" - to an extent, that's nonsense. Stuff like body language and voice tonation and whatever can and do have a place and can improve your game (especially body language if yours is particularly bad to begin with). But really, the most important thing is to get the girl actually having fun with the conversation.
Now from what you've said about yourself above, talking about yourself could easily get people to have fun. I'd love to hear some of the stories you must have, I'd find that very interesting and would enjoy myself listening. Yep, people do like to talk about themselves. People have fun talking about themselves. So yeah, ask questions about the girl, of course.
But think about other stupid conversations you've had. Perhaps the best examples are of flirty text messages. Often you talk shit, you repeat yourself, you are making everything sexual and putting loads of

symbols in there. Read it back. It's a terrible conversation. You would probably never try to have a conversation like that. But you both had fun whilst doing it.
Right, I'll stop rambling, but my two final tips:
1) Mental attitude/mindset. I think just going in planning on being a "cheeky chappy" is massively important. Think about being back at school, there were two types of "naughty" kid. Those who just got in trouble, and those who seemed to charm the teachers and even when they were being naughty would often get away without any serious consequences (think Zak in Saved by the Bell). Think about those flirty texts where you go in with the mindset of being risque, making sexual innuendos and jokes.
Go into conversations thinking that you're going to have some fun with the person. You're going to wind them up a little bit. You do this in your own way - your own personality shines through. Some people might tell actual jokes to do this. Others might be a bit more sarcastic. Whatever.
But go into the conversation planning to have fun yourself BY sort of being cheeky towards the other person.
NB: This is still the case, in my opinion, for all but the very most serious conversations. Even if you're having a fairly deep conversation about aspirations and stuff, it's still good to have this 'self amusement' type mindset. Obviously tone it down the more serious the conversation gets. So in a very flirty conversation, you might have every line or every 1 in 2 lines as the cheeky chappy line. If you get on to career aspirations or something, you might knock that down to every 1 in 3 or 1 in 4. If you're talking about how their grandmother died last week, you're probably going to want to think very carefully about doing it at all! But you get my point. Self amusement, cheeky chappy persona, put your own sense of humour forward as often as possible. Start at this point and tone down if it gets serious - don't start low and try to build up. It's much easier to start in cheeky chappy mode and work down if it gets serious than it is to start low and build up.
2) Actually use text and online messages etc. more as practice. Now I don't advocate using these as a replacement for in person practice. Not at all. BUT they are pretty useful when you have this "conversation management" type problem. The thing is, you don't need to think of anything witty straight away, you don't have any awkward silence. For all the other person knows, you're just making a drink. So it lets you think through how best to respond to a certain text in this 'cheeky chappy' persona. It helps you get some ideas, and get into that mindset. It's then much easier to think on your feet and act in this way when you're in person.