Here's how I tie down (assuming that tractor is a mid size machine)...
Four 3/8" chains, one at each corner of the machine. The chains all have a hook on each end. The semi-guys will use a G-80 chain, but that stuff is almighty expensive. I don't like using two long chains because this just isn't as secure as 4. Besides if you break a single chain or something comes loose, then you just lost total control of your load. With 4 chains, you have some redundancy. Redundancy saves lives, so it's a good thing. Why chains over straps? Well, the chains are stronger and more cut resistant. I've cut way too many straps to trust them on a heavy load. I save the straps for a load that's likely to shift so I can take advantage of the strap's capability to grip and stretch.
I then use two ratcheting style load binders, again 3/8".
The first step is to position the load on your trailer. You have to try and estimate it's weight and place it correctly. You don't want all the weight on the axles because the trailer will sway horribly with out enough tongue weight. You also don't want too much weight on the hitch because this will unload your front axle and it will have very light steering. More than one time, I've stopped and repositioned a load that I set wrong. I sucks to be repositioning a load, but it's better than losing control. The goal is about 10-15% of the loads weight to be on the tongue. For a 10k tractor, this would be about 1,000lbs.
It's very important to remember that chains only work in tension, this means they always have to be pointed away from each other. If the chains are ever positioned like this: //, then the load only needs to shift slightly for the chains to go slack. NEVER allow the chains to look like this: //.
Slack chains are weak because there is an opportunity for them to be tensioned suddenly, whipping them and increasing the effective load on the chain by several times. Chains must be so tight that they "sing" when tapped. If they don't sing, then you need to make them tighter. This is why I like the ratchet style binders over the lever kind.
When looking at the front or rear of the load, it's best if you come off the far side of the tractor and then cross the trailer. When both chains are installed, they would cross and form a X. Often, this isn't feasible so the chains look like this /\. Never like this: //.
You must come off a very strong point which has sufficient elevation to provide good angles. If the tie point is too low or too close, then the angles will be too shallow to provide effective control. For me, approved equipment tie points are the best, but wrapping a chain around a frame or axle will suffice. Just be sure to check for brake lines and wiring. Chain loves to eat these things. Typically, I find myself adding hooks and D rings to pieces of equipment that doesn't have good tie points.
The tie point to the trailer must be equally strong. D-rings are great, but only if they are adequately anchored. I've seen 5/8" D-rings welded to 1/8" plate steel. What the heck is that going to hold??? For a D-ring to work, it must be welded directly to the frame. My trailer has 1/4" stake pockets on the sides and I like to tie to them. I'll drop the chain through the pocket, come back up on the outside and then drop the hook onto the pocket. The 1/4" plate fits perfectly into the hook and this way I don't have to worry about it coming unhooked when I'm chaining.
Once you have both ends of the chain attached, stand back and look at your lines. Are they /\? If so then good. Check to see what the chain may get caught on. If the chain is caught on something, it may tension and then release when you are driving causing the chain to go slacked.
Because I only have two binders, I'll drive the piece of equipment so it can tension the chain on one end. I'll then put both binders on the other end. To get this to work can be difficult, so frankly it would be much easier with four binders. I like to place the binders in the center of the chain and pull from both ends allowing the center to go slack. This isn't as strong as pulling one end of the chain towards the other, but it doesn't damage the chain as would happen when it's being forced to bend over something. I never hook the binder directly to an attachment point because invariably there is a weird angle at the end of the binder.
When you are done, you should stand back and think about how the forces would be applied to your load. If you get hit in the front, will the back chains restrain your load? If you get into a nasty sway, will the side chains stay tight? Many people say you should visualize your load as being hung from the trailer, upside down. A bit overkill, but a great way to approach the concept of chaining. If you have it so the tractor can be hung from your trailer, upside down, then you've done a good job chaining. Yea, I realize the tractor may weigh more than the trailer it's attached to, so maybe you are really just attaching the trailer to your load instead of the other way around. All I can tell you, that when things get ugly, the cops have never written a ticket for having properly secured a load.