Honestly, don't think it's THAT obvious. Rapping and song writing has a very specific science to it that you somehow still cannot quantize. All you can do is watch what other people do- their techniques- then try to use them with your own spin put on it...
I've been writing and recording rap songs since I was 14 and it was, it was something that just came naturally to me... The gift of gab just came real coolly and easy to me because I'd spent my life listening to hip-hop and rock or metal lyrics and singing along. Get obsessive. Rap along to all your favorite emcee's flows and memorize their songs but don't put yourself into one lane. You don't want to be the guy that sounds like Eminem. You don't wanna be that Jay-Z guy. That is lame. Don't pigeonhole yourself. Listen to more than just the genre you like the most. I get a lot from punk rock, beatnik jazz poetry, and psychedelic rock lyrics in my general outlook... Those are just side ******* though... Hip-Hop is my baby mama so I treat her right and help her raise the baby (my own career) we had together.
Yeah books are great. Consult a thesaurus regularly... I read a lot. I read lots of diff random shit that I like on my Kindle- and then use the dictionary to define the new words. I wouldn't get TOO verbose though. Lots of emcees make that mistake coming out the gate and you can tell they used a rhyme dictionary or something. Rap is a very verbal and rhythmic thing. Don't just be all like "I GOT THEM ATROCITIES FROM ISOSCELES HIPROCRACIES N HIPPOCRATES PHILOSOPHIES". No one knows what that means because like, I just came up with that as a joke and it doesn't really make sense at all.
It's okay to be dense but make the big words you use interspersed with the rhyme schemes that are built up with lots of little words... and make references. If you like basketball or something then you can be knowledgeable enough to say a clever punchline about your favorite player or the game itself... I'm something of a book worm, movie buff and crate digger so I often make references to those things.
I draw graffiti. When I was a lil hooligan I ran with graffiti crews and shit. I enjoy to find the right beat, freestyle to it get a feel for a topic, then draw out a graffiti piece and notes for proof of concept, then sit down and write. Rehearse and edit the written to the beat as needed. Make certain inflections at certain parts in the beat... Record when you FEEL GOOD. Try your best to do everything in one take... otherwise most of the energy gets lost in trying to re-record and you get bored...
I drink lots of coffee and take nootropic supplements or narcotic stimulants, and chain smoke cigs when I write bars... or I'll write after a dissociative or psychedelic trip... I might sip a 40oz of OE or have a drink or 2 of Hennesy when I'm recording vocals... Lots of people enjoy freestyling on weed, but I don't smoke anymore. I'm not gonna advocate drugs to you but generally they work for me. I use them as tools though. It's a little hard to make a rap album when you're drugged out all the time. Being sober is very important- so in my daily life (i'm self-employed and a full-time starving artist) I just stick to coffee, tobacco, and supplements...
Be true to yourself. If you wanna rap gun bars but you don't even own a gun or know anyone that bangs IRL, it'll seem p fake if you make a song about murdering a bunch of fictional people UNLESS u create a character. Create lots of characters! Make up jokey, hokey characters about people in your life and then you can rap from your view of their perspective. but if you wanna be urself rapping, then rap what you know- even fictional story tracks you should make it clear to the listener that it's either tongue in cheek or from your imagination...
Stop telling the listener you are going to kill them or do this to them or do that to them... unless you're speaking to a real person in the song. Don't be too obnoxious unless that's what you're going for. It all depends really, on the track you wanna make...
FREESTYLE MORE. that adds to your ability to write on the fly. You think Kool G Rap or Jay Elec or Black Thought got to their level of professionalism in the studio by just staying in their head and note books? Nah. Try to find a balance in your freestyling and writing abilities... personally? I'm Okay at freestyling. I can mess up a lot. I'm practicing everyday and have been for the past 5 months or so and i've seen the improvement to my ability. I spent like years, on and off, JUST writing but now? Since I have that ability I've been able to go to a bar and cypher everyone there that rapped, get dap, and make them all think I was a huge, drunken jackass but mos def put non-rappers in their places.
You should be ready to recite material whenever.... Use a metronome when you rap, and rap on various types of beats. Try diff rhyme schemes and flows. That will help you get more connected and practiced with mfn time signatures and becoming a human instrument... Be able to make a trap song AND a boom bap song. Channeling the correct feel and bounce of the beat is very important to a great song...
Just be clever. Be witty. Be loud. Be confident. and BE TRUE.