Golden rule - never leave pins floating.
In the specific case of control pins, they are there for a purpose, they change the way the device works so you must do something with them. Look at the data sheet for the device and see exactly what the pin does, then decide whether it should be tied high, tied low or actively driven.
In the case of the 74HC245, the OE pin effectively disconnects all the output pins so it can be wired to a bus. If it should be driving all the time, you can safely ground it so the outputs are permanently active, otherwise it should be driven from a logic level so it is only enabled when required. For most logic families, it doesn't matter whether you tie an input directly to supply or through a pull up/down resistor but adding a resistor can sometimes be helpful because it gives you a node you can temporarily change while testing or as a debugging aid.
Brian.