If you live with the people you’re planning on feeding, you might be able to assume they’ll be around when the food will be ready. If you can’t, ensure they know when it is, that this is going to be the result of several hours of work, and that small pets may be at risk if they aren’t there. Know how many people you’re cooking for. Know if any of them are vegetarians or in some other way picky eaters, and plan around this.
The food is what you’re going to cook. Generally for a roast there’ll be some kind of central large meat dish, some smaller other-meat stuff, a couple of carb-based things, and some misc veg. For the purposes of this, I’m doing Lamb, Boiled new potatoes, Roast potatoes, Yorkshire puddings, Carrots, Cabbage and Stuffing.
The single most faffy and annoying thing you can cook for a roast dinner is Roast potatoes. They’re nice, but they take effort. Meat is generally “Prepare, tinfoil, roast for 80% of the time, remove tinfoil, roast for 20% of the time”, with the percentages and the preparations changing. Preparing lamb doesn’t need much more than plugging it with some sticks of rosemary, Veg is generally boil/steam/cook, serve. (Roast potatoes are boil potatoes, heat fat/oil in heavy roasting tin, flash fry potatoes in roasting tin over heat, roast in oven for 45 mins or so). The hard part about Yorkshires, assuming you know how to make pancakes, is reconciling the required temperature of them with the required temperature of everything else when you only have one oven.
So, you need a plan.
Take a piece of paper, and draw a series of parallel lines. Assign each dish a line, and the far right side to be dinner time.
You have the time when you want everything to be ready, so work backwards from that. After being removed from the oven, the meat should stand a little while in a warm place to relax a bit, so allow a little while for that (how long depends on the joint. For a large block of beef, you can probably do most of the vegetables, the Yorkshires, and the second half of the roast potatoes while it sits). Remember this is cookery and not a science practical, and you can fudge things five minutes either way so you have time to finish each task. Remember boiling pots of water takes time, how many stove tops you have/need at any one time, and how many shelves your oven has.
That’s really it, making a roast isn’t actually difficult, just complicated. It needs a plan.
(Things that went wrong this time: Carrots were out of date and icky, Overcooked the potatoes for the roasts – my mental map for cooking them is based on a different variety – leading to Roast Mash, didn’t pay attention to oven space leading to minor tetris minigame, oven didn’t heat up properly due to user-fail, Yorkshires burnt a little on the bottom due to losing at tetris. Huge mountain of washing up. All guests enjoyed the roast anyway, so – make a note here – huge success).