@OP: Best is to practice many different tactics (such as in Tactics Trainer) and recognize the recurring patterns. I wouldn't recommend practicing 700 puzzles per day (!), but 10 per day is a good minimum. After failing a problem, you should go through the solution and try to understand each move, noticing the patterns of the tactics. Positions with tactics are virtually limitless, so diversify and practice as many different tactics as possible, without getting burnt out on tactics training.
an effective way to study tactics

It's better to understand the position and see what is going on. If that means 100 puzzles 7 times then its meant to be...
If anyone knows Phelon who plays here, i got the idea of going through each book several times until you can get answer within under 15 seconds. he went through 2 books like that and it got him a 1800+ uscf rating from 1500, within 7 or 8 months.
By the way, Phelon is now 2000+ uscf , he also done a 3rd book the same, which must have gave him another boost. By doing other things along is the best way to not get burnt out.

Chesstempo.com
You will see huge improvement after few hundreds of puzzles. I recommend doing standard tactics first - then try blitz. Your standard rating will be probably much higher than blitz (mine standard is 2002, when blitz only 1740, but I am progressing). It certainly pays off.
PS: I will be 1700 soon, when I finish my first online game.

For sheer volume chesstempo, but for understanding, calculation training, and noting themes, motifs, and kinds of tactics look at LeMoir's How to Become a Deadly Chess Tactician. It covers simple silent sacrifices, complex silent sacrifices, preparing to sacrifice, sting in the tail, etc.

The best server to practice tactics on is books.
Granted this is just my own opinion, but I like to be able to flip to whatever specific theme I want to work on.
As to the question of whether it's better to do 700 one or 100 seven times one is just as good as the other in most cases because the patters will repeat. Once you pick up the pattern of how a rook and bishop can mate in a corner it probably doesn't matter if you see the same puzzle seven times or seven different puzzles with that same theme once. What matters is that you see the idea and are able to figure it out.
Others may have differing opinions.

100 puzzels 7 times (Not literally but this method is more effective for anything you learn because a opening prep you learned is useless if you cant rember it in OTB play).

The best server to practice tactics on is books.
Granted this is just my own opinion, but I like to be able to flip to whatever specific theme I want to work on.
As to the question of whether it's better to do 700 one or 100 seven times one is just as good as the other in most cases because the patters will repeat. Once you pick up the pattern of how a rook and bishop can mate in a corner it probably doesn't matter if you see the same puzzle seven times or seven different puzzles with that same theme once. What matters is that you see the idea and are able to figure it out.
Others may have differing opinions.
agreed
I have heard from different players that there are different ways to study chess tactics. So is it better to do 700 different puzzles or 100 puzzles 7 times? I want responses from players rated over 1700+ , since you have experience in that area and have tried different approaches! thanks