I'm m7 Warwick with almost 120k points and I have a 100% win-rate, And i'll be telling you the Do's and Don'ts while playing Warwick, and also what you should be building in different situations;
1-Skill leveling:
Warwick's most reliable damage and healing source is his Q, so naturally you would max it out first. The order for maxing his abilities out is the following: Q ,E ,W ,Q ,Q, R, E, W, Q, E, R, W, Q, E, W, R, E, W.
2-Jungle pathing:
What I like to do when playing Warwick jgl is to start Machete, Talisman, and start blue buff because of how mana-hungry Warwick is early. After you get blue buff, finish blue jgl side (Wolves, and Gromp) which will make me reach lvl 3 which can allow me to gank someone (try to prioritise top-lane over other lanes). When going to the red-side, start red buff then go to raptors, don't go to krugs unless you really need that extra xp or gold, because krugs waste a lot of time which have been potentially used for ganking. Another thing to know is that you can solo dragon lvl 5 which can give your team a massive advantage early on in the game, but remember to make sure that the enemy bot-laners don't have vision on you so that they don't kill you and take the drag. Try to gank allies as much as possible, because Warwick has one the best ganks in the entire game, so don't put your massive potential to waste
3-Runes:
Since season 8, I've been trying out a bunch of runes to test out which ones give me the best advantage so that I can win the game, and I've found the perfect runes which can be used in every single game:
Primary; Domination( In chronological order)
1- Dark harvest: One of my favourite runes in the game, it just works so well with Warwick because it helps him deal a lot of damage and still stay tanky.
2- Cheap shot: Synergises well with Warwick seen as you have 2 forms of CC in your kit, giving you the bonus true damage to win almost any fight
3- Eyeball collection: Cuz you get AD by destroying wards and getting kills, what's there not to like?
4- Ravenous Hunter: More lifesteal over an already absurd amount of lifesteal? Fuck yeah!
Secondary; Precision
1- Legend: Alacrity: You basically get attack speed for getting kills, which will help Warwick a lot when dueling.
2- Coup De Grace: Helps Warwick a lot when going against tough enemies such as Udyr and Jax seen as they deal a lot of damage, and getting that bonus AD will definitely help in fights.
4- Build:
I came up with this godly build which helps me get atleast an S- in every single game. This build can be used in almost every single situation; whether you want Damage, The enemy team has a lot of AD, or if the enemy team has a lot of AP, this build will work no matter what. Build the following items in chronological order:
1st item: Blue smite into cinderhulk. Make sure you rush this item first before getting Tiamat so that you have a lot of sustain and deal big damage early game
2nd item: Titanic Hydra. Amazing item on Warwick seen as it helps you in many ways, such as helping you clear jgl faster, giving you more sustain, and it also gives you insane damage because 1- Your Q and R deal on-hit effects which means that you can proc the active effect.
3rd item: Spirit visage. One of the best items to get on life-steal based champs such as Vladimir and Warwick because of the Unique effect it has which Increases effectiveness of all sources of health restoration by 30% meaning that your Q, passive, and R will heal you for more which is why this is a must build item even if you're against an AD heavy team (because spirit visage gives magic resistance)
4th item: Trinity force. Hands down one of the best items you can build on Warwick seen as it gives you health, on-hit damage, and attack-speed. It's basically Warwick's mid-game bread and butter.
5th item: Blade Of The Ruined King. The 2nd best item on Warwick, after trinity force, because of it's unique passive which says that basic attacks deal 8% of the target's current health bonus on-hit physical damage. Your Q and R both deal on-hit effects which means that the passive will also apply on both of the abilities, meaning that your Q and R will hit like a truck. What I like to do after getting this item is to Getting my dark harvest ready and activating my Titanic hydra active then using my q on an ADC, Which will literally 1-shot the ADC (if you have over 200 dark harvest stacks) while being extremely tanky with insane sustain.
Now for the 6th item, you get to choose which one of the two you want to pick:
Hextech Gunblade: for the extra burst damage.
or
Warmog's armor: for insane health regen and tankiness.
Pick which ever one suits your situation the most.
I hope you learnt a lot from this guide and I hope to see your win-rate improving over time.
but never buy 
. You should always buy Tiamat first back, even though you'll sit on it for a while. You should prioritize it even before your smite upgrade item. Warwicks whole clear is dependent on that item.
. My favorite item is 
since it'll give you the movespeed you need to run in and make a play.
Max W first rather than your random pick anything rank up
You can gank and invade at level 3 and be able to fight most other junglers, or flash fear w your gank which forces them to flash or die. Sometimes even both
to 
next. After you even have Tiamat and Bamis you can fight nearly any champ if you've farmed and ganked properly to stay relevant