So you have reached 100 and are ready to start on your final legendary weapon/class items, here is what I do.
Select your new LI's, remember that if your going for the absolute best, you need 1st ages with the correct passives. If your less picky, there is no reason most folks can't get by with a 2nd age or less than ideal passives. Keep in mind that not having a 1st age may hinder your ability to get into high end pugs who can be very picky about who they invite. Passives are different for each class, but often the morale and crit are the most desirable. Worry less about the actual legacies you get, but higher starting tiers and the correct legacies for your class make a little less work later.
Now you have your LI, do the following:
1 Equip it
2 Make a plan for what you want as final legacies. Check here: https://www.lotro.com/forums/showthread.php?568112-Complete-legacy-listing-(except-bridles) and/or here: https://lotro-wiki.com/index.php/Legendary_Items for what legacies are available and what they may become after you imbue the LI. Plan on seven legacies and make your list.
3 Level it to 30 selecting the best legacies for your class or the highest tier legacies. Either work. My rule is to take a T5 ot T6 over a better legacy that is only T1 or T2, but it is your call.
4 Check and see what legacies you have compared to your plan. Replace any legacies you want to change at this time. Get replacement legacies by deconing level 100 LI's that are over level 30 or from the store. Most replacement legacies are T2 so I only replace those that are low level. Stat legacies are T4 so that gives you a bit more leeway in selecting what you want. Remember, you can make more changes later, after you imbue so you don't have to be perfect yet.
5 Once your satisfied, level the LI to 60.
6 Apply 3 Anafalas Starlit Crystals, available as drops, quest rewards, barter from Epic Battles, festival rewards, AH, hobbit presents and from the store
7 Apply Anafalas Empowerment Scrolls to bring all legacies to T6. These are available from dailies in several areas including MT pre-battle, featured instance runs, skirmish camp, quest rewards, and the AH.
8 Now your ready, imbue that LI.
9 Use Scrolls of Legacy Replacement to finalize your legacies. These are available as quest rewards, from the AH and the store.
10 Add a 7th legacy slot by using a Anfalas Crystal of Remembrance, available as a rare drop, hobbit present, AH or from the store.
11 Apply a Anafalas Scroll of Delving, this should raise the available levels for your legacies. Available from drops, skirmish camp, AH and the store.
12 Start leveling your LI again.
13 Apply Anafalas Starlit Crystals and Anafalas Empowerment Scrolls until the legacies reach there max tier. Current max is 63 for the first line and 79 for your 7 legacies. Keep in mind that certain classes may not want to max the top line. As an example, if you are strictly a DPS RK, your class item gives outgoing healing, you may not want to cap this, the call is yours. The same goes for the lower 7 legacies, there may be some that you many not want all the way up. As an example, I have the Do Not Fall This Day Cooldown legacy on my fire stone, but over a certain level all it does is increase a healing skill that I don't have in fire stance. It's safe to leave that at the point the cool down is maxed.
14 Level your LI until you max out your legacies. When they reach the max, the bar turns gold, when the LI is completely maxed, the top bar turns gold.
15 Relics can be applied at any time but I usually leave it to last. You will need to select the relics you wish to slot. The best current Settings and Gems are available at a camp near Dingarth. The best Rune is from a barter vendor in Skarhald. You can also make runes at a Relic Master. How you play may determine which runes you want. Check them all before you decide and keep in mind you can change later if needed.
16 Craft and apply a Crafted Relic to your LI. You will need to be maxed in a crafting guild to have access to these and the best are bound to character. Every craft gets the same ones, you just need to select the one you want. You craft an item which can be traded at the guild for the appropriate legacy box. Open and slot. These just are not that powerful right now, but every little bit helps.
17 Final thing, you need a title. These change the base damage and or give you other enhancements. They are obtained by barter from vendors around Middle Earth. The best are currently from DA or if your short of coin there, the same ones are available from Ringlo Vale. The other set I see used are from Snowbourn. Some of these have a stat on them. Select carefully, some go on class items, some go on weapons, make sure you have one that works with the LI your looking to apply it to.
Notes:
1 I opened all my LI slots and keep them full with 3rd ages which I level to 60 and decon. This gives me a large number of relics that can be combined to give me the T9's and T10's relics if you want to use them till you get to the final set.
2 Shards can be made by deconing spare relics that you don't need, but if your short, make the crafted relics. The lower one on each tier is not bound so you can send them where they are needed. The upper one is bound and require a tome (available at the skirm camp), but the shards are account wide so even your level 30 cook has the potential to generate a fair number of shards for you.
3 Anafalas Scrolls of Delving and Empowerment can be melded at the relic master using shards, but the cost is ridiculously high.
4 You can mix up some of the parts like adding relics and titles before you imbue. Titles can be over written and relics can be removed as needed both before and after imbuing, I just generally wait until last.
5 What legacies and relics are by your class and play style. Ask someone with the same class and play style what they use (if your going to be an AOE champ, find one to ask about the legacies if you need, just remember not all champs play AOE and the ones that don't won't have the legacies you want). Relics are often to complement your class or to enhance a specific need, for a guard, I select Block relics, but a champ will want Mastery or Crit relics.
6 This is how I do it, but there may be some refinements to the process that have been introduced since I last made an imbued LI, it's been a while.
7 This was updated on 3/10/19. Changes include the new Runes as well as the current legacy caps.