Save up 100+ medium refines, then use them all on a lvl 4 item. This will get it directly to level 7 under most cir*stances, into advanced refine territory. I leave other items at level 4 until I have another 100+ medium refines in a different refine event.

This is how i do it, not sure if best way. Upgrade 1 item at a time as far as u can to make use of the wishing credits. I stopped at 9 though cos goin from 9 to 10 is pretty hard even with the wishing credit help.

If starting from scratch then i upgraded all the equip of my 1st position ninja and 2nd position ninja to +6. Then next event i took my 1st position to +8 and some to +9 to use my advanced runes whilst taking my 3rd and 4th ninjas to +6.
The reason i keep at +6 is so u c*e the next event to give u wishing credits for the +7 to +8 jump to help u save on advanced runes which r the most expensive

Look at your financial situation, identify your final ending point (for f2p, this will be either level 7 or 8 typically), then level an item straight to that endpoint.

Note, advanced are significantly harder to obtain compared to meds. Therefore, instead of leveling an item to level 7 and holding, sometimes (for the good gold initiate items), you might consider holding at level 6, so that once you have enough advanced runes (150 worst case) to get from level 7 to 8, you spend the meds to level 7 so you can get the advanced rune credits.

All in all, its a personal decision though, you need to see how fast you're gaining runes and plan your strategy.

after

After how much time the refinement Event Starts? Any guess?