LINE Chef is a time management game. There are 3 different mission: Score, Serve and Like.
Score stage - score a certain number of points
To gain higher score, increase the score given by each dish and the combo. Combo will continue by giving the customer 1 dish before the combo time gauge runs out.
Delay giving the last item to the last moment until the next customer walks in to extend the combo time. You can always prepare the food in advance and serve based on your own tempo to make full use of the combo time.
Use buddy with combo skills to help increase the number of combo.
Towards the end (usually the third level of the restaurant), there will be certain score stages that can't be complete just by using skills. You will need to use item. Usually these items will be given to you free so you don't need to spend any diamonds or cash. So do remember to save your item till then.
Serve stage - serve a certain number of customers' dish
This type of stage is the easiest. Even if your customer is angry, it is fine. Just make sure that you serve before the customer leave in anger.
However, there will be time when you serve everyone but it still doesn't reach the number of items required. In this case, there is nothing you can do but to keep playing. Each time you play, the customers and items will change, so the number of items will be different.
Like stage - serve customers before their satisfaction gauges get too low to get Likes.
It will be best if you serve customers based on their sequence, but it can be hard to keep track once there are more customers. So, my advice is serve the first dish of two or three customers first. The satisfaction gauge will decrease in time, every time you serve a dish, it will increase.
When you reach a difficult stage, consider using the sweets that you saved up. (The sweets will be given to customer with the lowest satisfaction gauge.) The sweets aren't very rare, as long as you don't use it often, it will be enough for this moment.