I realise this question is already answered, but I feel there are a few points needed for clarification.
- ask yourself if fragmentation is really causing you an issue? Fragmentation is only really a problem when reading from disk. Cache all your data in memory, and concentrate on statistics maintenance (link). Depending on the size of your database, if you can't cache it all in memory do you have a resource problem (e.g. RAM), as opposed to a fragmentation problem? Could your server be getting a high volume of hard page faults, and you don't even realise it?!
- How big are your indexes? If your indexes are less than 8 pages then they will be stored in mixed extents, and no amount of index rebuilding is going to solve fragmentation... move on!
- What keys are in your index? If any of the keys use something like 'uniqueidentifier', especially as the first key column, then I'm afraid you are unlikely going to solve fragmentation. Due to the nature of this data type, no sooner than you have rebuilt your index, it will be fragmented again after the first few inserts... that's the nature of the beast unfortunately.
- If you decide that fill factor is a route you need to go down, DO NOT set it globally for all indexes. Doing so could actually make performance worse. Fill factor increases the free space on index pages, ergo making the indexes larger in size. For an index that has an incremental key, reducing fill factor from 100 (or 0) will likely hinder performance, depending on the size of the index, because you will be causing SQL Server to read more pages to acquire the same amount of data.
Index tuning is a science, there isn't a "one size fits all" solution, so when you ask "should I aim for a fill factor of 90%", this is a genuine time when "it depends". I already posted this link above, but I really recommend you read it, to understand the impact fill factor has.
There are tools out there to help you on your quest (and I don't mean the Database Tuning Advisor!!!). sp_BlitzIndex is the one that I have stuck to over the years... hence my numerous links to their websites!!! :-)