What level are you now? Probably the best thing to spend in this game is £20 on crystals when you start, buy extra refils every day and get a couple of level advantage over your shard and take a good rank every day at your payout. The earlier you do that the better.
Otherwise when there is an offer with a guaranteed amount of shards for a character that will make a difference.
The emperor's demise bundle may be worthwhile to a newer player at the moment who want to spend. Shards of 3 characters needed for cls event and 2 required by lstb.
Personally i spent a bit when i started my account and havent spent since.
