Chrono Trigger

• There's really no way to screw yourself permanently. Most of these tips are just about convenience.

• If you reach the End of Time at a low level, you meet the frog form of Spekkio and can fight him at his weakest.

• The Soda Guzzling game is a good way to build up a lot of Silver Points/money early, especially if you have a turbo controller. There's a man in a tent over by Lucca's sideshow that trades your Silver Points for Gil. You can then use the Gil to buy a Lode Sword from Melchior before you visit Lucca's sideshow.

• You can flee from battles and the game won't tell you how. Many battles happen because of external factors or you stepping on certain avoidable tiles.

• When you get the ability to open the mysterious black boxes, go to them in the past first, say "no" to opening them, then go to the present and open them. You get an upgraded version of whatever was inside. You can then go back to past to open the black box. Although it should cause some kind of time paradox, you get to keep both the upgraded and original item.

• There are multiple sidequests in
  12,000 BC
  that can be lost forever past a certain point in the story, so try to do those first.

• Directly after the Ocean Palace, put Ayla in your party.

• Ayla has upgrades to her Fist weapon, but it is level locked and occurs very late game, if you even want to grind so much.

• A certain enemy appears in several places in 65 Million BC when it rains and he drops great stuff to forge with.

• You're going to get asked at one point to open one special chest; a chest containing a weapon, or a chest containing armor. Take the armor.

For the DS version only:

After you beat the Ocean Palace, there is a new dungeon that opens up called the Lost Sanctum. It's a pretty awful sidequest to be honest - the best rewards you get from it are right at the beginning and right at the end. So if you want to do it, do just the start, or all the way through. Be warned, the rewards completely break what's already a fairly easy game right in half.

Other than that, it's pretty much the same with an improved translation. The Dimensional Vortex part also helps bridge the gap between CT and CC.