I've had a little line in my backyard for about 3 years now. I've built and rebuilt it numerous times to fix fuck-ups, and to make it bigger as I've progressed. A few of the lessons I've learned:
Put a little roller or pump down or something just before the first jump (about 10-15 feet). It helps establish a rhythm.
Make the first jump really long and low. I'm at about a 10 foot gap, and my lip is about 2 feet tall. It's a really mellow angle (about 30-45 degrees). It's also got about a foot of step up.
Speaking of step up, give everything a little step up. It makes the landings easier to hit smooth. Contrary to common sense, a step up does not make the jump harder to clear. When I say I have a 10 foot gap, the actual gap is closer to 8 feet, but the point on the landing level with the top of the lip is 10 feet away. My step up extends the landing about 2 feet closer to the lip.
Make the landings way too wide. Most of my bad crashes came from missing landings. Also put a way to get out of the line between each jump.
If your line is good, and you don't suck, you'll build more speed with each jump, so size accordingly. Each subsequent jump should either have a bigger gap, or be slightly steeper. My three jump is about 10 feet @45, 10 feet @60 and 8 feet @~75 (I ran out of room), but I'm working on extending the last jump to about 9 or 10 feet.
Berms fucking suck. They use a ton of dirt, they are really hard to place right, and if the radius is too big or small, you can't pump them. They also use a ton of tarp to cover, and if you don't cover them, they get slow really quickly. Go really steep with berms because you can keep them shorter and use less dirt.