- At the end of a formal letter or a certificate:
Rome, 29th July 2014 GB
Rome, July 29 2014 US
You don't need the article (the) or the preposition (of) . You can use the 'th' (but be careful to get this abbreviation right -1st, 2nd, 3rd etc) , but it isn't necessary.
- A meeting:
The meeting is on the 29 July 2014
We will meet the 29 July 2014
I’ll be there the 29th of July 2014
I’ll be there on Tuesday, 29 July 2014
These are all British English - with the day before the month. Americans put the day after the month, and don't use 'of'.
Any of these are possible. The only one which I have deleted is the phrase with 'in' - dates/dates always use 'on'.
The shorter forms (without on/the/of) appear more businesslike.
- A period:
He successfully attended the workshop from 21 to 25 July 2014
He successfully attended the workshop from the 21th to the 25th of July 2014
Again, both of these are possible, but I'd prefer the first, because it seems more businesslike. The inclusion of the/ 'th' and of make it seem more conversational.