I tie mine on with a bit of thin cotton. The cotton eventually disintegrates, but by then the plants have got a firm hold on the wood. Anubias and java fern both hate being planted in the substrate, and their roots will rot if buried.
Stem plants like elodea and wisteria can just have the stem-ends in gravel. Wisteria can also be floated, it makes a great betta-hammock and puts out lots of roots. When mine get too 'hairy' from that, I plant them. Wisteria apparently doesn't much like alkaline conditions, though, which is maybe why some people have trouble keeping it alive. It's often mistaken for water sprite, which has a habit of melting when mature.. so make sure to do your research before you go shopping!
Planted tanks are kind of exciting and plants can be every bit as addictive as fish. I love mine to bits. Got a 40 gallon starting up this week.. and tons of plants to put in it!