make sure you use PHARMACEUTICAL grade PG/VG of whatever you buy. Other lower grades have impurities that may be harmful in inhaled.
The easiest and safest way is to simply purchase a zero nicotine bottle of e-juice from a reputable vendor of either unflavored (unflavored will dilute the taste), the same flavor, or if you have multiple flavors get a light flavor that will mix well w/ the majority of your juice. I do a lot of coffee and vanilla type flavors and I have found a light cream flavor goes well with almost everything, even fruit like apple. Doesn't really work w/ menthol though.