If you're new to engine swapping, have an assistant handy to help guide (and watch) as the old engine is removed and the new engine is installed. Most importantly, make certain that a good engine hoist is secured to the engine with a suitable chain and strong bolts (typically Grade-5 or better installed deeply) and washers to keep the bolt heads from traveling through the chain link and releasing the engine. If an engine drops from a hoist, the 500-pound hunk of falling iron will do more than change your attitude for the day. Don't rush this step.
One of the most efficient ways to install an engine is with as little on it as possible. This basically means that the final assembly on the hoist is the long-block, intake manifold, oil pan, timing cover, valve covers, motor mounts, balancer, and distributor (optional). This keeps the engine light and manageable during the installation. During installation the headers can be slipped into place, and once the engine is bolted in, the carb, water pump, and other accessories can be installed. A second way is to install the engine and transmission in tandem. This can work well, but you should have a few engine-only swaps under your belt first.
After the engine is lowered into position, tighten both engine mounts before releasing the hoist. This is because you may need to lift and slightly move the engine across the frame mounts to align the motor mount to the frame brackets and install the mounting bolts. If your fuel system will use a mechanical fuel pump, it may be easier to first tighten the motor mounts before adding the fuel pump. This will allow more access to the right (passenger) side mount.
Two other reasons it's generally better to install the crank pulleys after the engine is in place are so that the pulleys cannot be damaged and to eliminate the possibility that the installed pulleys might reduce clearance during installation.