Experimental design principles include having a clear question, using comparisons/controls, replication, randomization, stratification, and factorial experiments. Good experimental design provides unbiased results through randomization and blinding, high precision through uniform materials and replication, and the ability to estimate uncertainty through replication and randomization. Sample size is determined based on the desired power, significance level, variability, and size of the expected effect. Consulting experts can help design efficient experiments that use appropriate sample sizes.