>> My goal is to get a CCIE Security after CCNA

Isn't the path is CCNA - CCNP - CCIE .... ?

Practice as much as subnetting as you can. Solve problems from internet. Keep on solving old dumps or any questions you find in internet. For any certificate exam, not only CCNA, don't spend 12 hrs a day. Spend atleast 1 to 2 hours daily. Spend more hours only if you find topic interesting. Get some job in related field if you want to go for CCNA- CCNP-CCIE.

If you just want CCNA certificate then spend some bucks to buy the latest dump, and few days is enough if you byheart and don't want to understand or practice in real life. If you find yourself lacking fundamentals on some or most of the topics, then buy a book and start reading that. If you could not find job to practice CCNA stuffs or more, then forget about getting into CCNP or CCIE.