There are some common pain points to the new Battle style of play, feel free to add suggestions that help folks new to them become familiar, and please correct any errors I have. (Some are redundant to other sources that players are obviously missing, and buried deep within other threads.)
The secret to getting into the Battle panel is shift-b. In the instance join panel, they are listed in the order you have to unlock them, in the Battle panel they are numbered. You can't do the group versions until you've done that one in solo/duo form first unfortunately.
Now first, don't expect to fight all the time, this isn't an old style instance, there are trained soldiers there to do much of the fighting. They can pretty much hold there own most the time, but you can help so they take less damage. You need to help to minimize problem MOBs to earn higher medals.
Second, everything with a floating label over it can be used/interacted with. Right click it (or left click and "use" key, or select nearest object/NPC key and use) to get a pop up window with buttons. Hover over the button to see what it does.
You might only be able to extinguish the thing if put on fire, or there might be greyed out buttons until you are higher rank, but there might be something you can apply appropriately. Multiple people doing the same thing do it faster. So if you see someone interacting with an object, don't expect an error like the rest of Lotro, jump in and get it done quicker.
It is confusing at first to know where to go and find side quest objectives. There are indicators the edge of your minimap. It helps to do your first Battles with a kinmate, or someone familiar with them.
To get to a side objective that's not right where you are, it helps to hop on an old style horse (or goat for cave).
Don't ride/go too far in the direction of the enemy, if you cross the invisible "front", you will be killed with no warning, there's no indication where that line is, but it's safe to be where soldiers are.
Promotion abilities that really let you do things come after you've done a half dozen or more Battles and have earned twenty points or so.
Promotion points only come when you earn a higher medal than previously for that Battle/quest.
On the main quest objectives, check the NPC and banners health regularly. If low, help them out, either heal it/them, repair it, DPS MOBs attacking them/it, debuff MOBs, CC MOBs, or force taunt MOBs off.
On the side quests, some require more character abilities/DPS, some require more running about to help.
There is a rope on the wall in Helm's Dike that takes you down/up (your horse can climb ropes, don't worry). In Deeping Wall you need to go into the side room (under catapult), turn to go downstairs. In Hornburg, stairs are blocked, but there's a hatch in the floor to get down, and rope to get back up.
Most of all, experiment! Unlike former content that had a binary win/fail outcome, Battles are generally forgiving (the raid size being an exception). Things can glitch and not go well despite your best efforts, yet you'll still be rewarded for your successes and those glitches will be absorbed by higher results. Next time you do the Battle, you may earn greater rewards now that you have more an idea what's going on!
PS: Not a tip as much as a setting change, at the bottom of the Battle panel there's "Rewards" with four medals/bars with little arrow/chest indicators. The default setting is to give you vendor trash instead of higher end rewards. Click the two little arrows above the highlighted chests to accrue your earnings into better rewards instead of cashing out vendor trash all the time.
PPS: For an in depth advanced guide to Battle side quests, see: https://www.lotro.com/forums/showthr...de-Quest-Guide