lies.

In my opinion you should not use to much diamonds as time passes people will be able to bless higher.

Lemme try summing it up for you.
First, choose the weapon you want upgraded.
Then, get it blessed to the god of your choice, as high as you can get it, because you can't bless it again after you prep it. Also, note that ever "+" on the weapon raises the wc and damage od the weapon by 1 point.

Then, choose a number of slots you'd like. At a low level, I suggest getting no more than 10 slots (basically 100 dias.) In the end, you'd want to save up around 676 dias, which equals 26 slots, which is the max you'll ever be able to handle.

Now, gather a Prepare Weapon scroll.

Drop the dias with /drop diamond, use /mark weaponnamehere, and then double click your PW scroll. Tada! You now have prepared your weapon.

The next step is the most important one, as it decides the future of your weapon.

You can either add on stat bonus scrolls, which raises the corresponding stat, though this is best used for raising wisdom and pow, to obtain relics from your god at low wisdom levels. Note, it requires a number of corresponding stat+ potions as well to use these scrolls.

Next, you can also choose to use EW scrolls, which count as if you blessed the weapon again, but take up slots. I'm not sure if you can breach the max +s you'd be able to normally get with blessings (by that, I mean at level 107 wisdom), but you probably can. Remember, this adds +1 wc, and +1 damage, and the effectiveness of the attacktypes raises. (Like, the potency of Ogma's poison.)

Next, you have IWD scrolls. Very basic. Just adds 5 damage to the weapon. VERY useful, and the most often used scroll, besides EAs.

Finally, you have the Lower Weapon Weight scrolls. As of now, they are rather useless since no one can fill enough slots to make this useful. You see, as you fill slots in a weapon, the weight of it rises. For example, my Inferno Sword weighs over 60 kg with 9 improves. This will become a necessity, when your weapons become so powerful they weigh more than your armor, though if you have sufficient str, this really wouldn't bother you.

I might add that (at least in my experience) IWDs add weight while EWs don't.

Also, you can bless prepared weapons if you do it yourself, as nobody else is able to wield them. I don't know whether and how applied EWs mess up future blessing.

If you want to change your weapon's configuration or number of slots, the only way to do it is to clean it (/mark it, then use the cancellation-spell). This way, ALL improvements will be lost - there is no refund in diamonds or scrolls already used on the weapon.

As for handlable slots, you can handle 5 from the start, and one additional for each 5 levels of physique. A player of level 19 can handle 8, while one of level 20 can wield 9. These numbers apply to the filled slots, not the number of open ones. If you have a weapon prepared and fill more slots than you can handle, you won't be able to wield it till your physique level is apropriate. You can always fill slots later, to "grow into" a weapon.

A LWW will decrease the weapon's weight by 20%. This may be useful to save weight for reasons of speed, but it's usually a very small effect. As the weaponspeed is not as such determined by the weapon's weight, it will not speed up it's swing.

Satrek, you can not bless a weapon further if you have already prepared it. There is something in the scripting which will not allow you to do so.

In RP terms, the Gods don't consider the weapon "clean" and will refuse to permit any further blessing. ;)

Believe me, you can - I know people who did and did it myself. Bless a weapon to a god with some +, prepare it, and come back later if you have the required levels to pless it again. The only problem is that you have to do it yourself, but it nevertheless works. That is, though, if you havn't applyed any EWs in it.

I'm certain I tried it on Debug myself, and it didn't work, but I can't remember for the life of me. :X

It worked for Sarid and me on GK, with prepared weapons without any EWs. That's mainly the reason I didn't use any, to be able to bless it higher at some point. Rumor had it that it wasn't possible to bless them up if they had EW-+s. Maybe I'll check that myself, too.

If you've already prepped a weapon, and you're ready to prep it again to a higher level, will you have to start from the beginning or can you just keep building onto it?

start from the beginning

You have to "wash" it. i.e. use cancellation on it. It will be reset to, say, factory settings, and all scrolls and diamonds applied to it will be lost. That's what makes it important to make sure you have enough slots on a weapon when preparing it ;)