I agree with the majority - don't mess with it. Methadone is a hardcore opioid. Small amounts go a LOOOONG way, and for a long long time. Being new to opiates, there may be some safety issues ie. it takes a LONG ass time for it to 'kick in' and if you aren't aware of this, or anticipating it you may take too much and overdo it. This would suck... also, if new to opiates/opioids you wouldn't be wise to mix it with anything else (like benzos for example, as many people choose to mix opiates + benzos... I do NOT promote this behavior..exp to new users) as the dangers are increased significantly.
If you want to try opiates (in general) try something shorter acting and with faster onset. I'm guessing you came into some methadone and just want to try it as a result. If you DO, just take a small amount, for example 5 mgs. Wait about 2 hours. See how you feel. Getting a tolerance to this substance is the opposite of ideal (then, that's true for anything.). Just ESPECIALLY with methadone. W/d's are a bitch.