I think these two are quite good:
Elementary Differential Equations with Boundary Value Problems (Edwards &Penney)
An Introduction to the Theory of Numbers (G Hardy)
For the bare bones beginner who either doesn't know or has completely forgotten all of his or her high school geometry,I cannot recommend more highly:
Kiselev's Geometry, 2 volumes,translated by Alexander Givental
I'd also highly recommend Givental's wonderful introduction in the preface of the first volume on the history of this classic book and what motivated him to bring the Russian classic to an English-speaking audience.
After that,there are basically 3 books you can't go wrong with:
Elementary Geometry From An Advanced Viewpoint, 2nd edition, by Edwin Moise
Euclidean And Non-Euclidean Geometries, 3rd or 4th edition (either will do nicely) by Marvin Greenberg
A Survey of Geometry by Howard Eves, 2nd edition(2 volumes)
Moise is the classic text that develops Euclidean geometry using the metric postulates of G.D. Birkoff. There are several other books that try and do this,but none do as good a job with it as Moise. Greenberg is a remarkable historical tour through the various geometries of the plane as axiomatic systems,from geometry pre-Euclid through 19th century developments of non-Euclidean geometries through a careful analysis of the Hilbert axioms.
It also has many pictures and many exercises of varying difficulty incorporated into the body of the text,so you really need to read it with pen in hand. Eves is an older,2 volume work attempting to do for elementary geometry what Birkoff/MacLane did for abstract algebra. Some of it is awkward and dated,but it has a lot of cool stuff in it you can't find anywhere else.
Those 3 are how you get started to me. And if you want to go on from there, it's time to read the awesome classics of Coexter. They are THE detailed textbooks on plane geometry-but they are best read in my opinion after mastering the basics.
Good luck!
Best Answer
It would help if you said something about your background and your goals. For now, you might consider looking at any of the hundreds of freely available analytic geometry texts in google-books. Here are three widely used texts from the early 20th century:
New Analytic Geometry by Percey Franklyn Smith and Arthur Sullivan Gale (1912)
Analytic Geometry by Maria M. Roberts and Julia Trueman Colpitts (1918)
Plane and Solid Analytic Geometry by William Fogg Osgood and William Caspar Graustein (1921)