Get the best light you can afford..........cheap ingredients = cheap and nasty results.
Write everything you do down for future reference.
Realize that there is a long learning curve ahead of you and don't expect Master Grade results straight away.
Never compare your results to other peoples achievements.
Start with photoperiod fems and not autos, photoperiod fems are much better for learning with and can handle a few smalll errors quite easily......autos are not forgiving at all and really do require advanced growing skills to get decent results.
Be satisfied with "doing it yourself", harvesting your own crop is THE reward.
Don't over feed, a little bit often is better than lots all at once.
Don't get suckered into buying every product in the Grow Shop, there are complete one bottle "grow" and one bottle "bloom" formulated frtilizers that will do the job just fine while you learn about how cannabis grows.
Seedlings do not need "humidity domes", they just cause weak stems and encourage diseases.
Avoid defoliation at all costs, it is never really needed.
Low stress training and "lollipopping" are my 2 favorite grow techniques, learn about these and it will increase your yields.
Be patient and most importantly......enjoy yourself!