I allways strugle with the transitions when im chaging time signature or tempo.

I normaly solve the problem with diving with the wammy bar, holding out notes or slowly changing the speed while ending the riff, or making the drums do something wild.
But the thing is that it never quite fit like i want it to.

What do you do, any sugestions on how to do them?
practice, practice, practice. i suggest using a metronome to get used to it. if you're going for sudden odd tempo changes like 140 bpm -> 112 bpm have the drummer give off a 4 count to go into it, when recording i recommend a click track that you can mute out so you can keep perfect time. when transitioning time sigs however that really is just knowing your part everything i've ever written that transitions between time sigs is usually pretty smooth so that you can't really tell there is a transition, again, i just recommend practice.