Start slow.  Work on consistency and balance at slow tempos.  Over time, increase speed slowly while maintaining consistency and staying relaxed.  Speed will come.

Sorry, but there's not a quick way to do it.  You just have to practice.  A lot.

Thanks guys, both of those ways worked. And I've slowly increased.

This has been discussed about 20 times now, but I know how frustrating double bass can be, so here's my personal advice… again. Also bare in mind that I'm not a master on double bass - far from it, I struggled a lot when I first started, and I'm still not as consistent as I would like.

Firstly, I found getting started on double bass was much like when I skateboarded. They used to have 'trick tips' in magazines, but you can't just tell people 'move this or that', I found the best way of learning double bass was reading for sure, but then nutting it out myself, you learn which are the good and bad methods... just a thought.

Anyway, this is my technique, and it may not be the best for everyone... but my feet are slowly improving...

First:
Positioning of the pedals: anything that is comfortable. If you can play slowly, not feeling any tension and it feels as if you can do it for hours, its a good start. The rest is pretty subjective, and I can't really help you there...

Throne: I personally like to hang my bum slightly over the back of the throne. This I find, takes some weight from my legs, and allows my ankles to flow more easily as opposed to holding your legs up.
For accents or accented double bass patterns, however, I move forward a bit so I can let the weight of my leg accent the drum when needed. Using this I can do 16th notes at 160bpm (not very fast I know) with absolutely no tension in any part of my legs, and my higher speeds (170, 180) I'm comfortable at.

Legs: I let my ankles do most of the work, because the muscles are smaller in your ankles. This means that they will always be quicker than your thighs, but the down side is, they take longer to develop. As I'm using mostly my ankles, I find that my 'shin muscles' are exercised, and this is where I feel the strain after long periods of practice.
I've had conversations with double bass masters, and I asked them which muscles do they feel are being worked when they practice, and both have said the 'shin muscle' (I don't know the right name for it). So I figure I'm on the correct path, maybe not, and any advice to me is greatly appreciated.

It isn't a good sign when you're tensing up anything, and I believe that goes for all ascepts of drumming - not only your fee & legs, but there probably is a use for it somewhere (passion?), I'm just yet to find a regular use for it.

I find practicing doubles and parradiddles when keeping a solid backbeat with my hands also helps. Try using Stone's Stick Control for you feet, and maybe get some videos, like Thomas Lang's Creative Control, and watch his technique… get a teacher, attend clinics, its all beneficial.

For the first 6-7 weeks of starting double bass I felt as if I couldn't get comfortable, this I think, would be the same for a lot of things when you're first starting out. About 4 months ago I started practicing french grip, and it felt pretty arkward, but now its natural... practice, practice, practice.

Also, Bart has a 5-minutre lesson on this forum, and the 'search' feature is pretty helpful... My technique isn't really in conjunction with Bart's, and there are many people who prefer his, so you might want to give his method a try too, and by 'try' I mean at least 1 month of proper practice with that techinque. You probably wont feel much change within 3 days...

GOOD LUCK. Double bass (I found) can be quite frustrating.