When finding representations of finite groups over $\mathbb{F}_p$, (i.e. homomorphism from $G$ to $GL(n,\mathbb{F}_p$), it requires many times presentation of $GL(n,p)$. What is presentation of GL(n,p)?

To focus just on the question of giving a presentation of a finite general linear group over the prime field (or other finite field), leaving aside the fuzzy connection with representations of finite groups: This can be looked at profitably in the broader setting of finite groups of Lie type as studied by Steinberg in the early 1960s, even though there is a little distance between general linear and special linear groups. For a "universal" Chevalley group such as a special linear group over an arbitrary field, Steinberg gives a nice presentation in section 6 of his 196768 Yale lecture notes, building on his earlier Brussels conference note (published in French). None of this material seems to be readily available online, unfortunately, though Steinberg's papers are collected in an affordable AMS volume. Attempts over the years to publish the Yale lectures more formally fell through. Steinberg's presentation is based on the BNpair structure, but with some refinements. Treating the finite general linear group doesn't require too much modification, but perhaps isn't written down explicitly (?) In any case, this type of presentation is transparent and has the added merit of leading (over commutative rings) to fundamental ideas in algebraic Ktheory involving Steinberg symbols, etc. Meanwhile finite group theorists involved with the classification of simple groups have made their own good use of BNpair ideas following Tits and Steinberg. ADDED: Notice at the end of Steinberg's section 6 (page 72) the simple explicit presentation of $SL_n(\mathbb{F}_q)$ given by his method. You could get this by taking shortcuts in his proof, but keep in mind that the case $n=2$ requires extra care. To get instead the general linear group you just have to add some generators corresponding to scalar matrices along with suitable relations. Nothing is gained in this approach by working only over the prime field, which anyway would be inadequate for most applications. 


It is straightforward to read off a presentation of $GL_n(p)$, and for that matter any group of Lie type, by representing it as a BNpair. For $GL_n$, $B$ is the group of upper triangular matrices, and $N$ is the group of matrices with one nonzero entry in each row and column. Each of these two subgroups has an easy presentation, and the axioms for a BN pair combine these into a presentation for $GL_n$. 


In line with commenters, I'm not convinced that your motivation for the question is well founded, but it's an interesting question in its own right. My impresssion is that finding reasonably nice presentations for finite simple groups in general is challenging, and there is probably much still to be learned. Perhaps the geometric "inside" view of finite groups still has room to develop, to catch up a little bit with the far more mature "outside" view based on representation theory. One place to start concerning presentations of finite quasisimple groups (from which you can work out $GL(n,p)$) is the work of Guralnick, Kanotor, Kassabov and Lubotzky, link text. They're focused here on profinite presentations, which only distinguish the given group from other finite and residually finite groups, but these may be what you actually want, and it seems that it's easier to establish simpler profinite presentations than ordinary presentations. I think chasing references and citations should lead you to the relevant material. 


This isn't a presentation, but this file gives generating sets (of size 2) for $GL_n(F_q)$ and other finite matrix groups. I think it's kind of awesome: http://talus.maths.usyd.edu.au:8000/u/don/papers/genAC.pdf 


Generators and relations for $GL(n, Z)$ (which answer the question over $\mathbb{F}_p$, as well) are given in Morris Newman's "Integral Matrices" (which is a wonderful book for many other reasons as well). Newman derives them in a completely elementary way, as well (no BN pairs), which, I am guessing, should appeal to OP. 


See MR1871620 (2002i:20068) Chiaselotti, Giampiero(ICLBR) Some presentations for the special linear groups on finite fields. (English summary) Ann. Mat. Pura Appl. (4) 180 (2001), no. 3, 359–372. 

