I had some of the same problems you're having when I first started mixing juice. The quality of your ingredients is the first key to success. If you're mixing from scratch I'd suggest getting some small bottles of nic juice, pg and vg from xtremevaping.com. I've tried other suppliers for those components and also done the walmart and hobby lobby trips, but the end result was just garbage, that no amount of flavor could overcome. I mix my 50mg nic juice with 20% vg and 30% pg as an unflavored base. This gives me 25mg unflavored juice.
Then I add 2 drops per ml of flavoring that I'm mixing up, usually in 3ml travel bottles. So that would be adding 6 drops of whatever flavor I'm in the mood for that day. It's simple easy and quick.
As far as flavorings go, I've used Lorann's, Perfumer's Apprentice and FlavourArt. Hands down by far the winner is FlavourArt. Not only does it only require a drop or two at a time, it's dead-on as far as flavor and smell and I often get complements when vaping in public even at how nice it smells. The gang at HappyVaper.com in canada are just awesome and I live down here in Tennessee and get my shipments fast and easy. As far as the Lorann's I like the taste, but it's too sugary and tends to kill my atties. The PA stuff I've still got on my shelf in a box cause it tastes like vaping vodka to me..no flavor..just that alcohol burn...maybe my tastes will change later.
In closing, I'll just say that it took me quite a bit of experimenting and tossing batches(very small ones), or combining them and diluting them and then continually fixing them to get it down to my present routine as stated above. I'm very happy doing DIY-juice though, because I found with all the store bought stuff, that there was just too much inconsistency and I never knew what flavors were gonna kill my atties or just be a waste. Hang in there...don't give up yet...it's really fun when you get the hang of it!