I used to work in estate agency for 12 years and my thoughts would be:
use people you like but seriously, if they are too nice and too polite they are probably not the most effective in town. Sad but true.
give Sole Agency for a set period, say 4 or 6 weeks, after which you reserve the right to give it to another or several other agents, making the original agent pull out all the stops to gain full fee within the timeframe.
I would personally avoid giving to more than 2 or 3 agents as it smacks of desperation to go into every estate agency and be handed the same property by everyone - you are likely to get silly offers this way or people will just be put off.
have a for sale board, they are effective - some agents will knock £50 off the bill if you have one - worth asking.
Go in, ring up, hassle the agent a couple of times a week to keep them on their toes. The clients who are a pain in the ar5e get the best treatment!
Get several agents in to get an idea on price, check zoopla etc, price keenly but not stupidly.
Remember an offer from somebody who has no arranged mortgage or who has a property to sell with no buyer, or whose buyer has no buyer, is not really an offer at all and refuse to hold your property for someone like this.
Good luck xxx