An easy way to trim your own hair is to try the two strand twist method. After twisting to the end, clip off 1/4th to ½ inch. Perform this on each twist until all of your hair is clipped. It is harder to detect split ends on natural hair but they do exist.
Great tip to prevent tangles while shampooing natural hair. For medium length to longer lengths- it is a great idea to put your hair in 4-5 loose braids prior to shampooing. Wet braids in shower then squeeze shampoo into each hair braid while massaging your scalp. Rinse well and apply deep conditioning treatment to each braided section, cover with plastic cap and sit under the dryer for about 15 minutes. When conditioning is complete, rinse hair, unbraid and comb your hair with a large tooth comb. You should have no problems with tangles if you go this route. Remember to shampoo and deep condition every 1-2 weeks.