Well when I was leveling the Arc there was a range of levels where 1st was more likely to get sniped, and a range where 5th would always get sniped, and now it’s at a lvl where it’s safer to get 5th filled first but could still be sniped potentially
If your GB is in the 'sweet spot' (i.e. the point where 1st with the 90% boost can lock a position for less than 190% of the base prize) you definitely want to do get your spots locked starting with first. Most of the time only reason to lock later spots is if you are trying to get those spots/rewards to guildmates or friends so they get the blueprints. Otherwise if you get them at 190% and someone comes over the top of 4th or 5th because they want prints then you've made more fps than you'll be reimbursing to the guildmates that lost forge points (in general if you want people to keep doing the spots at 190% then they'll expect that you'll keep them protected from being sniped and losing fps).
Always fill highest to lowest.
Only add just enough points so that spots lock.
Unlock new levels with bps one at a time and only when you are ready to work on them.
For the profit zone levels (especially around 40) consider making sure 1.9 donors are online prior to unlocking the level. At the very least, only unlock and post it when people seem to be most active.
Unlock one level at a time when you reach the profit zone.
Some guilds I've been a member of had a thread specifically for GBs in the profit zone. You'd ask for 2nd and 1st and only unlock the level when donors for both spots were available and waiting. Others just asked in the regular 1.90 thread or in the guild's main thread.
Otherwise, secure one spot at a time - secure 1st and 2nd and ask for donations. Once filled, secure 3rd and ask again. Then 4th and when it's filled, secure and ask for 5th. This way, no one can donate less than 1.90 to lock themselves in a spot. Avoid the temptation to secure all spots at once. I learned it the hard way.