Hi I am KobiKB (Oceanic) and I am a top/jg main.
Playing 1000 ranked games this season I have progressed from Bronze 5 to Platinum, i found Cho'Gath to be the strongest carry of Solo queue due to his strong damage and natural tankiness.

Make sure you focus on CS as much as you can, last hit as much as possible even if it means the enemy top laner will get a free hit on you, you will manage to regen the damage from your passive and feel free to poke them with your W.
When near level 6 I always try and have to enemy below 300 Hp so as soon as I hit level 6 I can flash and Ult them.
If the enemy top laner is a problem ask the bot lane to put a deep ward down in their lane so you can teleport behind the enemy bot lane for kills. Teleport and feast are also useful for securing dragons with the team and baron!

At about 20 minutes into the game, placing a Q on the enemy melee minions and then using W on a full creep wave will usually clear it, your passive will also regen a lot of the mana used.
Don't forget you can feast big jungle creeps as well as scuttle, make as much use as the jungle as possible then you do not want to over extend in your lane.

Tip 1. Try to predict enemy movement to decide where to put your Q, also try and land W on as many of the enemy team as possible as the silence is OP.
tip 2. When your kit is on CD you can still do decent melee damage, but in a team fight it is not always best to melee on CD and may be more beneficial to kite and position until it is back up.