Editing Warhammer 40,000/8th Edition Tactics/Space Marines (section)

====Character Buffing====
For those of us that want a pure marine army it is important to double up on your force multipliers at every opportunity. The Troop Tax is no more; it is replaced with the HQ tax. Use your HQs to their maximum. And while HQs and the Lord of War Guilliman improve your hitting and wounding, units inside the elite slot have created a new dynamic for Marines. The Marine Formula -- a Unit and it's accompanying support Unit, goes for all the non-character models. 
*Ancients are must-takes in infantry-heavy Space Marine armies. Ancients enable out of turn shooting from models you'd otherwise be removing from play, even on your opponent's turn and help reduce the toll of Alpha Strikes: getting shot off the board Turn 1 is a thing, and Ancients help you recoup some of your losses by returning fire as models die.
*Apothecaries are best described as a trap, unless you're looking to fill out slots for detachments. the inability to revive heroes, the bad odds at returning lost models, and the loss of the once cool 5+ FnP in earlier editions is down right heartbreaking. maybe with the Chief Apothecary upgrade they could have a use, but in general avoid them. 
*Build around your Warlord! HQs like Kantor, Shrike, Vulkan, and Khan can drastically change your army's peak efficiency. Using Vulkan around loads of Melta toting marines is more efficient than Kantor around the same loadout. Conversely, Kantor with dedicated heavy assault troops (Assault Centurions, Assault Terminators with Thunder Hammers, Vanguard Veterans with Thunder Hammers, etc.) can take out a Knight in one turn of CC. Without Kantor, they only accomplish 50% of the damage. 
*Another popular combination is a Captain (ideally upgraded to Chapter Master if you can spare the CP) and Lieutenant; the Captain allows hit re-rolls of 1 while the Lieutenant allows wound re-rolls of 1. Hellblasters and Devastators in particular really benefit from being inside these auras. Chapter Masters and Lieutenants are essential for getting accurate firepower; other armies lack accuracy but make up for it with volume of fire. Marines will usually have a low model count and so need each shot to work.