You can say for example
- ぜひパーティーにいらしてね
- そのうちまた是非お出かけください
- 「今晩お伺いしてもいいですか」「ぜひどうぞ」
and
- きっと来てくださいね
- きっと訪ねて来てください
I would translate both ぜひ and きっと in these sentences with "by all means", but I'm sure (as always), there's a nuance in meaning when you use either. Could someone please explain this nuance? Thanks!