#1
I've made some pretty cool riffs but, have a hard time connecting them, got any suggestions?
#3
This is where the hard work comes in. Riffs are pretty easy to come by but to put them together you gotta put in a bit more work,

Be sure you know what you're playing. Analyse the notes and chords if any. Figure out what key they're in and where each riff resolves.

You may need to modulate from one key to the next so might need to write a connecting part. If they are in the same key and tempo you need to pay attention to how they affect each other.

If you can write some underlying drums or bass lines or other accompanying parts to your song that provide consistency it will help the listener feel the riffs fitting together better.

Sometimes the riffs might better fit in different songs from each other.

Like Jak said soundclips or even some tab might help more specifically.
Si
#4
Another thing just as important as the key is the tempo of the riffs. Though many more complex bands (Dream Theater, for one) often have tempo changes, the simplest and most common way of writing a song is to have a single tempo for the entire song. Play each riff to a metronome, see what tempo they are at and tweak the speed of one of the riffs to fit the other. Sometimes this works, sometimes it doesn't.

However, as mentioned above, this will very rarely result in anything musical unless the two riffs are in the same key. You can use theory to write songs with key changes (a la Dream Theater), but I'm assuming you don't know that much theory because if you did, you could probably come of with a way of conecting your riffs.
#5
What tiger said really hits the nail on the head as far as analizing and figuring you key and tempo that will definatly give you options to expirament with. Try to figure out if your riff is accenting certain chords or is in fact a chord progression.

Aside from this expiramenting in a relaxed and fun way is really helpfull. I think its hard to come up with something when you try to hard. You probably came up with these good riffs by just playing around for fun right? Try to get a drum beat or a friend and play with (drums bass rythem guitar doenst matter) and play the riff over and over and then try to go on to the next part without thinking to much. Get into a groove with you riff and dont force it and you just may hear something in your head or your fingers might magically find the next part. Especially if you know the key and some theory knowlage is laying around in your subconcousness.