On is correct. you would use for in that sentence if you're telling the listener what you're having for dinner. like "We are having pizza for dinner on monday"

about prepositions and conections,i can't say all here because there are too many thing to say while time is limited.You can add me like a friend(i'm so glad to be and help if i can^^) Back with your example:"i'll have a dinner with my wife on Monday" *We often use "on+days of week(monday,tuesday,wednesday,...)/date(Ex:...on wednesday February 22nd 2012 ) /...on the first of June,on christmas day,"... *we use "in+month/year(in february,in june,in april...in 2012,in 1992,...)/in the beginning,in the morning,in the afternoon,in the weeken..." but notice with"on the morning of the 6th"-not use "in". *we use "for+a period of time" in the present and past perfect tenses.Examples: -I have just learnt english for 2 months. -He had been her best friend for many years before you came here. Do you understand?

On is correct. With time: on days: on Monday, on my birthday. in months and years: in July, in 1968. at special days, at Christmas, at the weekend. Although you say 'I'm going on holiday', you say 'I went to Spain in my holidays (holiday is often in the plural in this sense). That has many different meanings. 'I want that cabbage.' The particular cabbage I want. 'I understand that you are busy.' What I understand. There are other ways that.it can be used.....