I have been on the island in August but not July. There are lots of Colombians on the island then, but not many foreigners. The weather can start to get a bit rainy as it is nearing their wet season but you may only see a brief shower here and there. The weather is extremely hot at this time of year.
I am not sure what kinds of things you are referring to when you say "have a good time". Since it is rather vague, I can only give you an overview of the entire situation.
The island and locals are not receptive to public nudity or "acts of lewdness" on the beach. They are also not very receptive to homosexuality, however this is starting to change a bit.
There are one or two strip clubs on the island for men but no legal prostitution. You will not see prostitutes on the streets or in the clubs.
You can buy weed from the rastas and smoke it in the open but you have to watch out for the tourist police.
Drinking and driving is illegal but it happens quite often by locals and tourists alike.