Meepo is definitely the hardest hero to play well.
The word well is emphasised because there is a difference between playing something and it working and playing something and completely destroying everyone.
Meepo has the potential to, and often will, break an entire enemy team in a matter of seconds, IF you can do it right.
If you aren't prepared to micro and practice hard, don't bother with Meepoing.
Poof is incredibly powerful, you want it maxed ASAP. Remember you can use it on yourself, so that you teleport nowhere and do double poof damage around you. (Leaving damage and arriving damage).
Geostrike is maxed second because it have brilliant stacking slow and the damage it adds it fairly nice too.
Your net is a great peice of kit, and the fact that it interrupts channeling means you get one point in it early, it means you can cancel some nasty ultimates, aswell as people teleporting to escape, other than that, its not as strong as other skills until later in the game, where you can chain 5 of them (1 per meepo) to enforce a total lockdown on a hero.
Your ultimate MUST be taken whenever possible. There is no exception to this rule.
This is only how I personally like to micro my Meepos it might not be the best way in existence, but it works fairly well for me, and I leave most games with 25+ kills and less than 10 deaths (it rarely goes over 5, but sometimes they have Gyrocopters or sand kinds who eat Meepos for breakfast).
I like to create 2 control groups. The first is my original Meepo. This enables you to switch to him immediately in order to use any active items on him when you need to. I then combine all other Meepos (EXCEPT the original Meepo) into a second group. The reason for this is blink-poofing, which will be explained later.
The best way to get off a fast, effective, group poof, is to press W, Click on the target, TAB and repeat. This will swap between Meepos one at a time and use poof, you can normally get all 5 to poof within about a second, maybe less. Once you give it a go, its not very hard, you are literally just mashing W, TAB and clicking.
To use your net, make sure you take into account its painfully long travel time, which increases with distance. It can be pretty difficult to land, but you should practice hard, and you'll figure it out eventually. There isn't much advice I can give other than to always aim ahead of a moving target. This can also be chained by the above Tab-Click spam, but you substitute your W for your Q.
Beyond this I generally use mouse control for any kind of splitting up of the Meepos or controlling them in different locations.
As a Meepo, you ALWAYS want the safe lane. This is because you want ready access to the jungle. Buy your first two items (Ring of Regen and Ring of Protection) and head to your lane. From there you ideally want some kind of ranged support who can look after you up to level 6. Anyone with slows is a brilliant combo as it allows you easy nets and thus can possibly secure first blood with a net and a poof.
Once you reach level 6 you'll have your first clone. This is a good thing! You can now decide between a number of options, which you will have to choose which is best for the time, although I'll try to give some decision making guidelines below.
1. Your team is having a good early game, and your lane is doing ok.
If this is the case, you should focus on jungling. Jungling as Meepo is incredibly easy once you have your ulti. Go to a pack, double poof, they all die, advance to next pack. There is nothing more to that. Make sure you keep an eye on the lane and take opportunities to gank or help your team mate survive.
2. Your lane is having trouble.
Stay in lane with both Meepos. This will mean you can 1 shot entire creep waves with a double poof, meaning you can push the lane easily and get a lot of gold while you're at it. Be careful you don't over extend and try to get some kills with net and poof.
3. Your lane is ok , but not as good as it could be. You are also confident you have good map awareness.
Split your 2 Meepos. 1 can jungle, the other can help the lane. Remember if one of your Meeps run into trouble, you can poof across the map to assist him and secure more kills.
This is one of the things that makes Meepo such an excellent ganker, but it takes a LOT of practice, and can backfire and leave you exposed if you mess up. Don't worry about it. No one gets these things instantly. It took me a good 2 weeks of practice, and even then I only land them perfectly 7 times out of 10.
Here is where your 2 control groups comes in handy. Quickly swap to just your original Meepo and identify him, maybe move him a little away from the others. Select your other control group, of all the rest of your clones, be they 1 or 4 in number. Quickly do your poof spam onto your original Meepo, you now have about a second to press your first control group, activate your blink dagger, and target your location of choice. This will mean that your first Meepo appears suddenly on the enemy hero or creepwave, and then is immediately followed by 4 other exploding Meepos, doing devastating damage and scaring the p*ss out of anyone nearby. You will almost always land kills with this.
The whole motion needs to be practiced until it becomes one fluid movement, you have to be able to do the whole thing in about 2 seconds for it to be at its most effective. Good luck!
Sometimes, you can misstime it. This will mean that only 1 or 2 Meepos ends up teleporting in, leaving you weak and few in number. You should try to immediately poof out again, or bring in the rest of your squadron as soon as possible to avoid a swift death. This will probably happen to you a number of times before you get it right. Keep trying!
People who you should be extremely careful with, are people with area of effect disables, or large area nukes. Warlock and Gyrocopter are the bane of my existence as a Meepo. Their ulti's will wreck you. Completely. People with stuns such as Centaur Warrunner, and Slardar, should also be treated with caution.
Finally, people who can easily pick off single targets. Pudge could cause problems, but if you are good, you can turn his hook right back on him, and poof to the kidnapped Meepo, ruining Pudge's fun. Huskar can cause problems with lifebreak, if he leaps on you and manages to nuke one Meepo down, all your Meepos fall. Be careful out there!