Just some ideas...
1) If you have joins, then remove a join at a time to see if that makes a difference. If it does, then the issue is with the joined table.
2) If you have no joins, then I would disable an element at a time to see if that makes a difference. Once you do this, you can focus on that element to see what may be the issue
3) If you have filters on a element that is responsible for the slowness, try removing the filter to see if that improves performance.
4) If you have filters on an element set to 'drop down' and you have that elements 'List View Settings > Filters > Filter Data' set to 'recorded data', this can cause Fabrik to perform queries against the database to get the recorded values. First removing the filter, then closely examining the indexes behind it and the setting related to filters for that element could improve performance. In these cases, you can try changing the filter type to 'field'. If that solves the performance issue, then it was the excess queries on each record to feed the drop-down that may have been responsible.
5) You can also go into PHPmyadmin and check the cardinality of the indexes on an offending field. I've had situation where I have stored a longish string but the index size for that element was much smaller. The string I was storing started with the same substring and the last characters contained the uniqueness. Once I used PHPMyAdmin to increase the size of the index, then the cardinality improved as well as the performance.