So I recently tried writing some of my own tunes (metal/rock) and I'm having trouble making riffs link together.

For example, I'm really having trouble getting a riff with its roots on the A-string to lead into a lower more thrashy riff with a lot of opens on the E-string.

I've tried letting the guitars and bass drop out allowing a drum fill to make the transition but I think that this too often takes away from the overall fluidity of the song.

Anyone got any tips or tricks to help me out?

Thanks lads.
well from what ive learned is.... If you need to switch from string to string just use an ascending scale, if that still doesnt sound right then change the tempo of the riff. If you have some more problems then just write a new riff inbetween the two!
"My guitar is not a thing. It is an extension of myself. it is who i am."-Joan Jett
Maybe include an extra bar or two and throw in some powerchords to transition to the lower riff.
You could change chromatically... another option.
Quote by AlanHB
It's the same as all other harmony. Surround yourself with skulls and candles if it helps.
B is the fifth of E, so theres a harmony there. Could include that in switching to the E string.
Understand nothing, in order to learn everything.

Quote by liampje
I can write a coherent tune ... But 3/4? I play rock, not polka.