First grow need help, suggestions and tips

Hi
I have just started my first grow
I have planted my germinated seeds in bio buzz light mix soil the seeds are lemon skunk from greenhouse 250 watt HID light system.
I was wondering how many times would i need to water my plants and how can i water my plants so i am getting to the roots as well as i recently had 3 gnomo automatic seeds the plants were very good on the first week but after the second week the leaves started to yellow and then the plants died i did kind of over feed them at times and i was not getting directly to the roots when i was feeding them i used a type of sprayer bottle to water them.
I am using nutrients but i was also wondering what type of equipment would be good to water them with so the water solution is getting to the bottom of the plant aswell.
And would it be best to stick to a 18/6 light cycle 4 the first for weeks of vegitive stage then switch to 12/12 for flowering.

water the plant when the top has a dry crust, stick your finger in 1 - 1 1/2 inches in the soil and make sure its dry aswell, then water. depending on the pot you have your plant in, you can fill a bucket (or anything your pot fits in) with a few inches of water, mix the nutes in with the water then place your pot in the bucket. Letting the soil suck up the water/nutes, when the top is wet take it out. good luck

hi mate.....greenhouse seeds lemon skunk has been in one of my tents for a while....its a big yielder and a good smoke...though it tends to hermie at high temps.....u will like it.....biobizz light mix is crap....use the biobizz all mix...(what i use) start your nutes at a quarter of the recomended dose....water when you can stick your finger in the soil as far as it can go and its dry.....also that theres no condensation in your run off tray...watering when the pot is totally dry(light) is too long(or when leaves wilt)...also biobiss soil is pre nuted so you dont need ferts for 2-6 week depending on light or all mix