I have some suggestions
1.) As Maltose66 mentioned, always try your flavor with pg/vg first! Its cheaper and you can add flavoring or vg to find your sweet spot. I highly suggest finding your sweet spot for each flavor you have. Make a test bottle, starting at a low percentage such as 5% to 10% flavoring in PG/VG and test, add flavor or PG/VG as needed and test again. Repeat this until you find the perfect amount for you. (document every drop or measurement you add!) I know, this can sound like a bit of work, but trust me it pays off in the end!
2.) Start with single flavors. Pick flavors that you enjoy to vape as is. My all day vape is vanilla bean ice cream with a touch of EM. Jumping into multiple flavored recipes right off the bat can be so frustrating when you start, they are more difficult to get right and many give up before they have even begun do to this.
3.) Pre-steeping is a new method many are promoting (you mix your pg and flavor then put the bottle in a baggie, dunk in a cup of hot water and let it sit for a bit to get the flavor to meld into the base.. add nic later, not before this!)
4.) Remember you are working with
highly concentrated flavorings! If it tastes horrible you have to MUCH!

Add more pg/vg and test. When its to weak you will be able to tell.
Cotton Candy or Ethyl Maltol is an awesome item for any DIY kit, it will smooth out your mix and adds for me that Yum factor
MTS Vape Wizard is also a great additive, it softens the flavor out and adds depth to your mix
Sweetner is also great to have on hand! There are alot of different products out there. Some people just like to add Marshmallow to sweeten as well.
DIYers cannot document enough! Most of us have made that heavenly juice and due to forgetting something never been able to reproduce it!
There is no perfect flavoring company, each one has something to offer. They are like car companies, you will always find fans and non-fans hehe!
The most important thing of all. Taste is subjective and its about you, so while advice is awesome.. trust your taste buds!
I dont wait to try my mixes, I know many do. If you use the pre-steeping method above, yes your e-juice will get better in time, but the time is lessened.
I do clean my palate in between test batches.. water, crusty bread, saltines or sherbet/sorbet are great for this! Think of it like fine wine tasting
