From Marrakech take a shared taxi to Imlil, cost 40 MAD per seat. The journey takes 75-90 minutes. The taxis leave from a small market 1km (2 blocks) south of the Bab-er-Rob, bus 35 from the Medina goes there. Taxis can be scarce after about 11:00. There should be no need to change transport at Asni as suggested in some older guide books or websites. In Imlil there is a mountain guide agency right next to the car park where the grand taxis are parked. Here a number of people will approach you either proposing the guide you to the refuges or to sell you a map. The maps are not very helpful and are quite expensive! It is perfectly simple to make the walk without a map or guide and to simple ask for directions on the trail if unsure.
From Imlil walk to the Toubkal or CAF Refuge, about 4-6 hours, straight up the valley through Aroumd and Sidi Chamharouch. A more interesting route crosses the low pass to the west of Imlil to Azib Tamsoult (keep high and head south once across the pass, 4hrs). Camp or stay overnight at the gite there. Next day continue up the gorge past an awesome waterfall and turn sharp left at a path junction (1.5 hours). Go right at the next path junction about 30 minutes further on. Zigzag up an enormous scree slope to a pass with superb views of Toubkal (3 hrs). Descend easily southeast to the refuges. This is a recently constructed route that isn't shown on many maps.
The ascent is on a good, well-marked path all the way. From the refuges cross the river below a waterfall (difficult after heavy rain). Scramble out of the gorge and follow a good path across a scree slope. Continue across boulders to a stream. Cross the stream and scramble up some rocks (cairned). The path makes a loop to the left, then a steep section threads through some massive rocks. The path continues up the corrie and zigzags up to a col at about 4000 metres. Turn left at the col. You can cut the corner here, but the views are better if you stay close to the ridge. After a couple of false summits you see the true summit with its steel surveyors' tower. Towards the top the ridge itself is difficult, so the path stays on the left (west) flank. Takes about 2.5 hours if you're acclimatized.
There are countless tour companies that can provide you with equipment and guides.
There are two big mountain huts at around 3200m altitude, right next to each other. You can pitch a tent here as well.
Even when only going to the refuges at around 3200m altitude sickness can be an issue. Staying a night or two in Imlil and at the refuges before ascending further can help preventing altitude sickness.