A few basic tips:
Listen to songs that carry out the style you are looking for, and try to make sense of what the structure is. You can even put it into your DAW to try to tempo-match, and then break it down into how many bars until each section is over. Where's the intro? Where's the outtro? Bridge? How are the dynamics changing over the course of the track?
Common transitions make use of cymbals and other transition sounds, or perhaps drum fills, but good transitions tend to connect both texture and contour (especially when writing orchestral, which has "only" organic instruments). Not just the density of the elements present, but also, the elements should feel like they're working together. Make yourself write a melodic transition sometime, and with time you'll hopefully develop that (voice-leading) as simply a core skill. You can do a simple melodic transition by writing a melody that sustains through into the next section, but later on, you could improve it by making all the little elements around the lead work together to lead up to that new section. For an example, I tend to share this, since it's what I consider my personal best arrangement. Maybe it'll help.
Have your friends listen to what you have and give you advice... including us. That means post a WIP, not just "help me".