Latem's kit allows him to play flexibly. However, remind that try to keep one loop on your hand unless your are in fight or trouble. Misuse of his ability could made Latem no loop to use and become weak in fight.
Since Latem is mana independent, he could sustain in lane for long time.
His passive Flexibility allows him to move faster upon casting ability. It helps him to kite or chase and enemy. Moreover when entering a melee fight, the extra damage provide by his passive allow him to deal more damage without using ability.
Making Cracks is useful for harassment. The knock up effect can disrupt some channeling abilities, although the duration is not long.
(W) Domesticate is useful to weaken and retain enemy in fight.
Latem's (E) Mutual Consensus grants him strong mobility to chase and escape. Moreover, his will get back his loop upon landing which give him chance to use more abilities.
With proper landing of (Q) and (E), Latem could enter a team fight surprisingly or escape from ganking instantly. Using (W) and then (E) will be useful to chase an enemy.
Latem's (R) can be a strong crowd control to a team fight. Moreover, each champion inside the range grants Latem extra damage output.
Using (Q) Making Cracks to focus an enemy and then rush towards it by (E) Mutual Consensus. At this moment Latem have to loops, by using (R) to retain the enemy, and then apply (W) twice to lock up your target.
This combo will deal a lot of damage to it and makes them difficult to escape from fight, if it conduct sucessfully.
As Latem's kit consists of appreciable amount of both AD and AP ratio. Therefore, items providing both AP AD will be effective. Also, building in to full AP as a DPS champion or into AD fighter Champion are both availabe.
Hextech Gunblade is a strong item for Latem. It privides both spell vamp and life steal besides AP AD, which give strong sustainabilty to Latem. The active also slow the enemy which alow him to chase off the enemy.
Trinity Force is a great item for him, as it privdes bith AP and AD and it spell blade works well with Latem'a (W). If the enemies comprise of great AD output, purchasing Iceborn Guantlet is considered.
Although Guinsoo's Rageblade privides AP and AD, it is less useful for Latem. Latem does not depends too much on penetration items as his ultimate provides him extra damage output in team fight.
However, as a fighter champion, Latem do not have direct defensive ability. He is vulnerable to crown control. Hence, Defensive items with health and tenacity are crucial for him. Mecury Treads is a good item protect him from crowd control. Spirit Visage is also good for him by providing health, magic resistance and some cool down reduction.
For armor, Sunfire cape is good for him by prividing him armor and health. Its passive is also useful to extra magic damage the enemy in melee fight. However, Randuins Omen works well too by its active that slow the nearby enemy. If the enemies comprise of great AD output, purchasing Iceborn Guantlet is considered as it gives CDR and a lot of armor with spellblade as its passive.
For AD Fighter, Start Dorans Balde Health Potions
Crucial Trinity Force Black Cleavers Mercury Treads
Offensive Last Whisper Ruined King Blade Hextech Gunblade
Defensive Sunfire Cape Spirit Visage Raidains Omen
For an AP DPS,
Start Speed Boots Health Potions
Crucial Zhonyas Hour Glass Ryai's Death Cap
Offensive Death Fire Lich Bane
Defensive Spirit Visage Iceborn Guantlet