Strong bridge with a tight flexed body, looking at your hands.
Neck kips (floor kips).
Floor Kip to Bridge.
Back extrension roll to bridge.
Back extension roll up a wedge, to bridge, to stand.
Get yourself a tumble track, learn back bounces to handstands.
From there, basically do a backbounce to bridge on the bar. When you can do that, put some padding where your ankles may hit on the bar, and bridge on bar, stand up, fall back to support over the bar. From there, speed up the process until you pop over the bar and do a tkachev on the tramp bar.
If you would like, an alternative is to not use the bar, but the end of the tumble track, and make yourself travel backwards into a porta-pit that is level with the tumble track.
To help with the turn-over, a solid pancake position will help a ton! Thout it is not necessary.
I cant think of too many other drills at the moment.. Im sure a few more will pop up...
Gymnast.com used to have a few videos in a series and called it a reverse hecht. The site is defunct but I saved them in flv format. All 6 are 31mb.
There are also quite a few articles on gymnasticscoaching.com showing drills for them.
Tumbl-trak.com has 2 videos with drills for the Tkatchev on a tumbl-trak or tramp.
If you want I can see about setting them on a public downloading service so you can download them. You need to have a FLV player and codecs to play them. Filesize is pretty small but your computer has to fast enough to play MPEG4 videos ( even my dinosaur of a computer can but it tends to bring everything else to a crawl ).
Does your gym have a belt? You get strapped in and get on the bars, then the coach will pull the ropes making sure you make it over the bar on the actual skill. If your gym doesn't have one I would talk to a coach about getting one they are very helpful.
The Tkatchev is a brilliant and complex skill that many gymnast learn to elevate their difficulty on both the Assymetric bars (for women) and the Horizontal Bar (for men). This skill is complex because of action of the body from a hollow position to an arch position the element requires for successful counter rotation of the body around the transverse axis of rotation (the flipping axis).
The most important aspect to remember in counter rotation from support in any given apparatus is not the angle of the counter rotation upon releasing, but the angular velocity with which the counter action is completed that will create a successful attempt of counter rotation. In other words, it is not guaranteed that a good bridge will allow for a good Tkatchev. What is more important is how fast the body can go from a hollow position - through a stretched position - to an arched position...The speed with which the body counter rotates is the main concern with succesful performance of the Tkatchev.
Many coaches put the accent of the Tkatchev's pedogogical learning process on the amount of bridge achieved upon release of support rather than the speed with which this bridge is achieved. The overall straightening and counter rotation of the body will stop once the gymnast releases from the bar, therefore if the speed of this counter rotation is not sufficient, then the gymnast will begin to 'hang' in flight and will not 'turnover' when completing the element.
Having mentioned the above biomechanics it is important to understand certain 'drills' that will allow practising of speed oriented changing of body shapes for the gymnast. There are many types of exercises that can be trained without ever holding onto a bar and will allow a gymnast the dynamic abilities of changing their shape from a hollow shape to an arch shape rapidly.
These exercises include, headsprings, back extension rolls to bridge rapidly, Courbette snaps (hollow to arch snaps of varying nature).
All these type of drills will allow for a rapid change from hollow to arch upon release. Do not get into the mindset that having a great bridge will allow for a great Tkatchev. I have seen many gymnasts learn a fantastic Tkatchev with a poorly executed bridge...I am not advocating that you do not need a bridge however, it is not the primary indicator of whether or not a Tkatchev will be succesful or not. What is lies with the gymnasts abilities to change his or her shape from hollow- through straight- and onto arch with high velocity.