It tends to remove metal contaminents. Even new tubes should be cleaned, especially if you have a dilute sample. Avoid stop-cock grease contamination, especially if you have peaks near 0 ppm. Use the right amount of sample. As the molecular weight of your sample increases, use the higher range of the sample masses given below.
Gels are a bad idea also.
Too much sample gives a poor quality spectrum. Use a deuterated solvent. Old bottles are often contaminated with water or other compounds. DMSO is very good at picking up contaminants. O if you're trying to obtain a 1 H sample that may have small peaks in the vicinity of the water peak.