My number one best tip is to get those stains under cold water as soon as possible and rub out as much of the stain as possible with your fingers, especially if the stain is banana or peaches. These are horrible because if left on to dry the stain will turn black, and after this is nearly impossible to remove.
I know stains usually happen away from the convenience of home, but I invested big time in bibs, and those portable stain towlettes and stain pens by TIDE and other detergent companies. I also would be sure to carry spare clothes on the road so that I could rinse and/or treat stains immediately. As soon as I got home, they'd go into the wash. Alot of work I know, but if you can get your little ones used to a bib during meals and snacks it helps alot.
Sometimes, while rinsing out a stain, if it is bad enough, I use a small scrub brush (like a finger nail brush) and rub in some Fels Naptha soap, or any basic lye soap bar (Ivory is good, even the very industrial and gritty Lava) to get as much of the stain out as possible. The key is to at all cost avoid letting the stain dry/set in. Be sure to rinse well.
If the items were whites, I'd use a Clorox bleach pen directly on the stained area, then wash. I avoid full-on liquid bleach because it will often yellow your items. It's a tricky deal with that pure liquid bleach..so I really like those pens where you can target the area.
If it's a colored item, I'd rub in either Shout! stick or gel, and use colorsafe Clorox.
If the stains are very light, I have had good success with a scoop of Oxyclean powder. I always wash stained clothes in cold water. It's better for keeping the integrity of the fabric and colors in tact, and more effective in getting stains out.
If your little one has sensitive skin, Dreft makes a mighty good stain spray that does a good job on breaking up the usuals like peaches, bananas, chocolate etc.
I hope this helps. This is alot of work, but I had great success in preserving all of our baby clothes. Most have been laundered many times, worn by more than one child, and are in pristine and in like new condition.