Firstly, both VG and PG are 'safe', and both can be mixed together, so no worries there. Ratios are a matter of personal preference, but a general rule of thumb is that The higher the VG,the thicker the juice, and the more vapour produced. The higher the PG, the thinner the juice and the more throat hit produced (bearing in mind that throat hit also varies with nicotine content). As for standard mixes, a standard VG mix is usually around 80vg/20pg and a standard PG mix, 70pg/30vg. Some folks feel that PG carries the flavour better than VG, but I haven't really noticed a difference. Thicker juices, ie those with a 100% or high VG content, do not 'wick' as well with top coil tanks/atomizers as the thinner juices with a higher pg content.