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. I've had good luck starting with a drop of saliva.
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.
Its best to secure the fitting in a vice but it that's not possible, then a small piece of steel rod can make it possible to hold the hose in the vice without damage.
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. 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).