Need nute help

Ok i wanna give my lady a boost seeing as how shes growing as slow as a snail going up hill. I have miracle grow tomatoe plant food and am atroscious at measurements and could use all the help given by u kind souls here at RIU. I wanna mix the right amount for a gallon of water but the last time i tried i burnt a plant so bad i ended up just pulling it up and starting over and the lady i wanna give nutes too i burnt her leaf last night with my light i almost cried(j/k). lol
All advice and ne help given is appreciated beyond comprhension.
K5
PS: shes around 21 days old and only on the third set of leaves.

i'd say use any nutes diluted between a 1/16-1/4-1/2 of recommended dosage depending on the strain...... like indica's will usually brown at tips but a thai strain will soak it up. id be carefull sum miracle grow is too rich in potasium for EG N.P.K 15-30-15, whereas you want something a bit higher in nitrogen and even in potasium and phosphate whilst in veg.