HI guys! I am a new DM but I have played for well over a year now and could do with some Hints and tips to running the campaign. I do have an excellent co-DM but he is also a player never DMed passed Goblin Arrows so I don't want to spoil it for him! Any advice would be great as I am also recording and putting the sessions on YouTube. 

Hmmm. Been a while since I ran that and I TPKed the party at Cragmaw Castle. 

A few thoughts...

I wouldn't give the goblins surprise during the initial ambush and I'd have one goblin flee down the trail in order to point it out as a path to a hideout versus just a random encounter. 

I'd skip Thundertree entirely. It's over a week of traveling and the encounter with Venomfang is problematic. I'd probably have the druid show up to save the group during the orc encounter. 

I'd add a few skeletons and similar to encounter before Agathas lair. I also gave the players opportunities to find other objects of interest to the banshee so they could each ask a question. Made for a nice mini adventure. 

For the encounter at Cragmaw Castle I'd replace the owlbear with a worg as it makes much more sense. Give some thought to the roof of the castle as my players first thought was to climb to the roof. I didn't want them climbing about the rafters so I told them the roof had caved in long ago and the goblins used hides as coverings. The hobgoblins hit really hard. Especially if the players are dumb enough to make a bunch of noise and pull the entire Castle. Depending on their party strength I would consider replacing some of the hobgoblins with plain goblins. 

I'd consider adding Venomfang to the encounter with the drow at the end. Seems like it would give that a little extra umf.

Hi thanks! 

I've kinda changed it up a little. so during the first session they kinda wiped out the goblins on the road, as I am only working with 1 new player, I have allowed them to choose characters of their own at level 1. They wanted to check to see if there was more goblins and they stumbled on the trail, hid the wagon and went off. 

As they choose their own characters I tweeked with the encounters (made them a little OP) in the Redbrands hideout. which is where they are currently barracked in section 2 storeroom for a short rest. Do you think its right as I now have 6 players...to add extra skeletons in the crypt and perhaps a goblin or two during the encounter with the Nothic? 

thanks for the advice on thunder tree, I was a little concerned reading through it. 

I am also working slowly on linking this adventure with Horde of the Dragon queen and Raise of Tiamat as I am homebrewing a part 3 to the books and it made sense considering Phandalin is on the Sword Coast. 

My group did pretty good with the Redbrand hideout. It might be kinda easy with a group of six. I added some dark mantles to the cavern with the nothic. Spiced up that encounter fairly well. I ended up skipping the skeletons as they don't make much sense to me and my group got pretty beat up because they drew most of the hideout after the first few fights.

I tend to have NPCs run for help or make perception checks to hear fighting. The players managed to squeak out of the goblin hideout and won out against the redbrands but they didn't learn their lesson and the Castle overwhelmed them. Those darn hobgoblins hit hard.

You can decide to add a few skeletons just before they hit the room. If they sailed through the redbrands then maybe a little extra encounter would work if they are too beat up forget about it. They should have a hard enough time with Cragmaw Castle later on.

I say group of six one player is having to drop in and out so technically its a group of 5 but they have some great stats hence the op redbrands, but then I almost killed three players in one encounter so do you think I play it by ear? 

I'd say that if you almost killed 3 of the PCs in the Redbrand Hideout then you are ahead of the challenge curve already. Remember that the idea of an adventure is to make it to the end. That doesn't mean you have to use kid gloves all the time (I did TPK my players after all) but if you are dropping PCs in the early parts of the adventure you might not need to beef things up as much as you are thinking. A couple easy things to do during an encounter or just before is to add a few extra hp or have an extra couple monsters run in from an previously unexplored room. 

My players died because of bad tactics. One of the players was a assamiar and flew (by himself) over the castle and into several rooms with the idea of finding some braziers to light some fires. Not a horrible idea but his assamiar wings are bright glowing things. While he was doing that the other PCs charged the front door. So the flying PC dropped into the kitchen with all the goblins there, fled and then dropped into the altar room with more goblins while the other players engaged in a pitched battle in the entry hall with goblins and hobgoblins. So they did two things wrong. They split the party and they charged in the front door. Even so they came close to winning. 

If your players are not using any caution and simply charging into fray then there is no reason to take it easy on them. On the other hand, if they are using responsible tactics and regularly dropping to 0 hp then I would recommend you dial things down a bit. Or at least save the heavy hitting for the 'final battle'. In this case Wave Echo Cave. 

I"m currently streaming Phandelver as DM every Friday with my group on Twitch. I had the most fun trying to homebrew some of the story details to make the game more interesting, since my group prioritizes roleplay over raw gameplay. I think the biggest change I did was to turn the Zhentarim woman in the Miner's exchange into a friendly goblin and playing her as the sister of Droop (the non-dangerous goblin you can meet in the Redbrand hideout). It set up the party to the idea that not all goblins are necessarily evil, which got them to approach Cragmaw castle more carefully, since they didn't want to just burst in guns blazing, and they had an interesting interaction with the goblins in the kitchen.