I'm afraid that we only have regular cokes.

Better say: I'm afraid we only have regular Coke. 

I prefer tenderloin than sirloin when I eat steak.--**Correct sentence~ ^^ 

Can you take me a plate the way you coming from kitchen?

Better say: Can you take me a plate on your way from the kitchen?

As a result that I have watched him, he always eats steak medium well.

Better say: As a result of what I've observed, he always eats steak medium well.

My mom will certainly keep me from home tonight.

Better say: My mom will certainly keep me from coming home tonight.

I don't like over midum eggs, but this restaurant always offers it on the foods.

Better say: I don't like over medium eggs, yet this restaurant constantly has them on the menu.

I want to assist you as a assistant.

Better say: I'd want to help you as an assistant.

Your job is assistant, so you only take care of your boss.

Better say: Your job is an assistant, so you only take care of your boss.

I missed the bus, and could I push back our meeting? --**Correct sentence~ ^^ 

I forgot my appointments and I made another, so I often rescheduled these days.

Better say: I forgot my appointments and planned another, so I was always rescheduling these days.