Environment is Number one.
Get yourself a hygrometer with min and max facility on it and you'll know what is happening in the tent when you're not around.
With LED's you want about 27c lights on, and no lower than 22 with the lights off. While they are still Vegging, humidity should be around 70% but when in flower you should be aiming for 50%. Probably a tenner from amazon.
You need an extractor fan, probably about a 150mm for a small tent, but this needs to be wired into a fan controller such as an SMS, which will regulate the fan speed depending on what temp is in your tent. When it gets hot, the fan speeds up, and when the desired temp ir reached, it turns itself back down to the minimum. One end of the fan should have a carbon filter on it to hide the smell as best it can and the other end should be vented out of the tent. Not only does this control temps but it also draws in fresh CO2 which is essential to growth.
Next you need a heater of some kind for when the light is off or its particularly cold. Oil filled rads work best. Again, you need a controller for the heater to turn itself off and on as required. G.A.S make a pretty good heater controller for about 50 quid.
These are the most important steps. You could have the best cuttings or seeds in the world, but if your environment is not right, they'll still come out shit.
Search google for Growell or greens horticulture. They do all the bits youll need