I would like to invite you to dinner tonight.	Do…	
I look forward to receiving your prompt reply	Look…	
Enclosed please find the menu for your reference.	.	.	I’ve…	
Kindly inform me of your schedule for the weekend.	What…	
I am pleased to receive your email on 12 November.	Thanks…	
I suggest having dinner on Friday.	Let’s…	
Kindly call me later today if it is convenient.	Give…	
We may go to an Italian restaurant. 	Why…	
Where shall we go for dinner? Do you have any suggestion?	Where shall we go for dinner? Any…	
I know a suitable restaurant near here.	I know…	

Some words to avoid an informal letter:	

convenient   suitable   request   receive    suggest / suggestion  kindly   inform  moreover  schedule  reference   

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Do you fancy going for dinner tonight?
Give me a call later if you get time.
I know a good restaurant near here.
I’ve attached the menu.
Why don’t we go to an Italian restaurant?
Let’s have dinner on Friday.
Look forward to hearing from you soon.
Thanks for your email. / It was great to hear from you.
What are you doing at the weekend?
Where shall we go for dinner? Any ideas?