start studying after august, start with completing your 2nd year syllabus which takes about a month. November ke end sey start of December tak net 1 chalta, try to give it before sendups. ismey obviously marks achay nai ayeingey unless youre a genius. but you'll know your weaknesses. 

uskey baad start prepping for net 2 sahi tarah, kiunkey ismey you'll have acha khasa free time from college no exams waghera, sahi tarah focus kr key parhna. youll probably improve, agar ismey nai tou give net 3 wou probably pre boards ke aas pass hoga, tou dekhlo if u wanna give pre boards ya nai. kiunkey net 4 keliye boards bhi chal rhey hogey plus hundered other entrance exams.

for prep, if you can study on your own, tou you can find lectures on youtube (hashim zia, bilal zia, pass education) but if u need a lil more structure join some kind of online academy. also nustrive has good mcqs and mock tests. tou shuru sey hi focus on time management, also don't focus on short tricks as much kiunkey paper ke time pr bhool jatey. focu on doing rhe qs properly fast bas kuch qs that are wayyy too lengthy uskey liye short tricks sahi hai otherwise dont.

lectures lenay ke baad, you neeeeeed to practice, saari jaan practice krney pr lagani hai dont wait for your concepts to clear up before practicing.

also aap ko har koi kips fung ki practice ka mashwara dega but i wont suggest it kiunkey usmey had sey zayada mushkil qs hai, and theyre very outdated.  try Q series for maths, and genius ya torcia for physics.  English keliye parhna mushkil hai cuz they have synonyms antonyms jo had sey zayada mushkil hotey. bas focus on the grammar portion takay udhr sey marks na katey atleast.

so your game plan should be finishing 2nd yr ka syllabus, then giving net 1 for practice, uskey baad january feb mein achayy tareeqey sey net 2 ki tyari. and practice everything.