If you are joining a Push-Lok fitting and the correct hose, you will find the two pieces don't just magically come together. There's a trick or two that has always worked for me and you might try these. Generally, there are two ways to go about this; either with or without a lubricant. If you're really concerned about your assembly, you may wish to do this without a drop of oil on the fitting. I've had good luck starting with a drop of motor oil but its not absolutely required.
No Lube - warm up a cup of water in the micro wave (about like you would a cup of coffee). Insert the end of the rubber hose into the hot water and wait 1 minute. At the end of that time proceed with the steps below but skip the motor oil.
With Lube - insert the hose into a vise. Either soft jaws or a rag will protect the outer covering of the hose. Lightly snug up the jaws of the vise so that about an inch of the hose is extending. Insert a short piece of steel rod - 3/16ths inch works great. While holding the rod, tighten up the vise - it doesn't have to be super tight.
Attach an old 944 fuel filter to the fitting and use it as a handle to push the fitting down into the hose. Slow, steady pressure works best. A drop of motor oil or liquid soap applied to the fitting barbs will make this a little easier. Remove the fuel filter and pull out the rod.
If your attaching a curved fitting, you will either have to let the rod drop out the other end of the hose or not use the rod. The danger here is that without the rod, your vice will crush the hose enough to damage the inner wall. Also, you won't be able to use the filter, but a simple pair of locking pliers will suffice.
A length of fiberglass sleeve makes for functional dress-up. The fit is a bit snug but the sleeve can be "pushed" on and then trimmed. Once in position, a good grade of heat shrink will finish things. Remember to leave enough room on push-on fittings for the clamp (don't clamp over the fiberglass sleeve or heat shrink).