Reply to original question:
Depending on how bad the original render is would depend on how to attack the problem. If it is loose, sounds hollow when tapped then it will have to come off.
If it is quite solid just loose pebbles then you can remove all the loose pebbles and give the render a good hose down. Next you need to apply your bellcasts, corner beads and so on.
You then need to apply a scratch coat. I always use 4:1:1 consisting of 4:1:1 (Sand. Hydrated lime Cement) Some people say there is no need to put a waterproofer in the scratch but i always do if i am dashing as it prevents the second coat going off too quickly giving you a little more time to rule off.
Apply first coat not too thickly and rule off with your feather edge. Give it a score with your devling float or scratch comb. wash off tools get to the pub and have a few pints.
Day2:
Hose down wall and let excess water run off whilst you knock up your gear. Apply second coat consisting of 5:1:1 (Sand. Hydrated lime Cement) apply your second coat forming your drip beads and features above windows . Rule off and while you are doing this your labourer would have washed off you derby spur or watever else you have decided to use and he will be stood behind you with the hurling trowel.
Now the end result is all down to wrist action, Be prepared for a sore wrist if you havent done this before.
This is a very basic explanation on how to do it. If you are 100% insistent on having a go, then i will explain a little better for you.
picture 1 shows scratch coat
Picture 2 showing top coat
This finish isnt dashed but rubbed up with a polly float and then sponged finish. No pebbles applied