The e-liquid you use will depend on the coils your kit takes. Generally, coils with ohmages higher than 0.6 ohms are intended for thinner e-liquids with either a higher level of PG than VG or a 50/50 split. A coil of 0.6ohms or lower will be meant for use with high-VG e-liquid that produces large clouds. Using the wrong e-liquid for your coils can result in leaks or burnt wicks, so be sure to check, as it will always be listed on the online product page and the side of the bottle in stores.