I haven't played a game of Warhammer 40,000 in many years and not since 2nd or 3rd Edition was I someone who won more than they lost. I just refuse to use dubious tactics and optimal lists. I field my models, my army, and I always make sure everything is painted first. One day I hope to paint some more models as I have many, many unpainted models. I may even play another game of 40K, the last games I played are detailed here, which I think is at least one edition out of date.
Basically I tend to advance. Nurgle is long range firepower deficient historically, but in the new rules who knows. But for tournament games I try to be smarter about this. For Vancouver I plan to get back to my older style of shooting at range especially against assault armies. I don't play Khorne (yet?) but I load as many models as I can in Rhinos and drive them across the board. Those on foot also advance. The demons arrive sporadically then make due haste towards the enemy. My lord watches for lascannons and bounds across the board, even my heavy support moves. The only armies I wouldn't advance on are horde armies. As regardless of how many rhino's I have, Nurgle is a bolter based army. Thus the range is 24". Actually 18" is the optimal range, 6" move and then 12" for the bolter/bolt pistol.
Since my luck is non existent and I often forget tiny details like smoke launchers or blight grenades, I feel the two most important post army selection decisions are initial setup and target prioritization. I usually pick out the most feared opposing squad/model and shoot at it until it's dead. I generally lean towards opposing heavy support elements early then switch to other annoyances often assaulting them in H2H where I like my chances against most armies.
I find how you set up models in 3rd edition and the missions an improvement over the previous editions. I feel I have more success in 3rd edition because of the missions as oppose to the old victory point system. I have to do better job on the table quarter occupying games though. You have to be really single minded for some missions. I have a lack of speed and a lack of long range weapons so advancing early is almost a must if you plan on covering the entire width of the board which for some missions is a necessity. I also have a reasonably versatile force and enough staying power to tough out the take and hold style missions. Early in the game I do my share of dieing (sometimes) but hopefully rally when the demons arrive and the H2H commences.
My actual set up is to give the best position to my most effective long range heavy support choice. I try to set up valuable items in cover. I try to eliminate opposing lascannon type weapons first to enable my lord to move around more boldly. Although there are no Vortex grenade toting veteran sergeants I know my deamon lord is vulnerable and worthless without getting into H2H.
I've given a lot of thought to tactics pre Vancouver GT. For my landraider, I'm tempted to move 12" on it's first move against most opponents. Then disgorge my retinue and stand and fire. If I get first turn I will likely not move it at all, to maximize my likelihood of eliminating the opposition anti tank forces. Terrain permitting, I now have the ability to kill stuff if I go first. Previously it was better to set up in cover and choose to go second.
I traditionally have more foot soldiers then all but the hoard armies (after GT Calgary and fighting 190 Orks I know what it is to be outnumbered), if not in pure numbers then in squad choices. Though with the new rules a lot of my "troops" count as elite or heavy support. I also plan to make use of the fourteen man squad rule in the future. The demons don't appear right away so the sheer size of the demonic host and their unpredictable arrival often causes fits for an opponent. I don't plan on using George much with the latest Chaos Codex.
The Nurglings basically cost nothing, do nothing, but count as a troop placement. So I use them to draw out a more important squad from the opposition. The Plague Marines are placed with an eye towards advancing. I usually give one of the cheaper squads the job of screening the valuable HS choices.
My rhinos I place close together as I want to overwhelm at the point of attack. My chaos lord gets placed last so I usually put him off on a flank away from the lascannon like contraptions. Hopefully the rhinos can roar forward delivering my assault troops into the teeth of the enemy. The Plaguebearers will arrive as reinforcements.
Once stuck in, it often comes down strictly to dice rolling. I'm not sure what the new assault rules will do to my thinking, regardless of rule changes with only 3-6 guns shooting over 24 inches one must advance. And it is always better to charge then be charged. I've given a lot of thought to the new rules. I'm pro shooting prior to an assault, cause I always spend points on special weapons. Two flamers should kill more then two extra H2H attacks, one would think.
Although I'm not sure how much it costs, nor whether I would pay for it, having most of my army being fearless ensures that they keep moving forward despite casualties which I probably rely on more then I realize.