correct fertilization(6-6-18 is tobacco fertilizer) or at least close to those numbers.
pest control- aphids, japanese beetles and hornworms.
keep the ground around them weed free as much as possible.
Suckers- these are the small shoots that come out from the base of the leaves,different than topping.
Topping is removing the flower stalks to encourage leaf size .
However, if you plan on saving pure seed- allow one plant to flower but put a bug bag (5 gallon paint strainers,paint section of local home improvement center)over it before it blooms ,secure the bottom of the bag with string to the stalk so no pollinating insects can get in and possibly cross pollinate.
Lay awake at night listening to the tobacco grow- yes it grows that fast.
check back to FTT every hour on the hour with pictures .